In the Linux kernel, the following vulnerability has been resolved: pfifo_tail_enqueue: Drop new packet when sch->limit == 0 Expected behaviour: In case we reach scheduler's limit, pfifo_tail_enqueue() will drop a packet in scheduler's queue and decrease scheduler's qlen by one. Then, pfifo_tail_enqueue() enqueue new packet and increase scheduler's qlen by one. Finally, pfifo_tail_enqueue() return `NET_XMIT_CN` status code. Weird behaviour: In case we set `sch->limit == 0` and trigger pfifo_tail_enqueue() on a scheduler that has no packet, the 'drop a packet' step will do nothing. This means the scheduler's qlen still has value equal 0. Then, we continue to enqueue new packet and increase scheduler's qlen by one. In summary, we can leverage pfifo_tail_enqueue() to increase qlen by one and return `NET_XMIT_CN` status code. The problem is: Let's say we have two qdiscs: Qdisc_A and Qdisc_B. - Qdisc_A's type must have '->graft()' function to create parent/child relationship. Let's say Qdisc_A's type is `hfsc`. Enqueue packet to this qdisc will trigger `hfsc_enqueue`. - Qdisc_B's type is pfifo_head_drop. Enqueue packet to this qdisc will trigger `pfifo_tail_enqueue`. - Qdisc_B is configured to have `sch->limit == 0`. - Qdisc_A is configured to route the enqueued's packet to Qdisc_B. Enqueue packet through Qdisc_A will lead to: - hfsc_enqueue(Qdisc_A) -> pfifo_tail_enqueue(Qdisc_B) - Qdisc_B->q.qlen += 1 - pfifo_tail_enqueue() return `NET_XMIT_CN` - hfsc_enqueue() check for `NET_XMIT_SUCCESS` and see `NET_XMIT_CN` => hfsc_enqueue() don't increase qlen of Qdisc_A. The whole process lead to a situation where Qdisc_A->q.qlen == 0 and Qdisc_B->q.qlen == 1. Replace 'hfsc' with other type (for example: 'drr') still lead to the same problem. This violate the design where parent's qlen should equal to the sum of its childrens'qlen. Bug impact: This issue can be used for user->kernel privilege escalation when it is reachable.

The remote Debian 12 host has packages installed that are affected by multiple vulnerabilities as referenced in the dsa-5900 advisory.

    - -------------------------------------------------------------------------     Debian Security Advisory DSA-5900-1                   security@debian.org     https://www.debian.org/security/                     Salvatore Bonaccorso     April 12, 2025                        https://www.debian.org/security/faq
    - -------------------------------------------------------------------------

    Package        : linux     CVE ID         : CVE-2023-52857 CVE-2023-52927 CVE-2024-24855 CVE-2024-26656                      CVE-2024-26767 CVE-2024-26982 CVE-2024-27056 CVE-2024-35866                      CVE-2024-38611 CVE-2024-40973 CVE-2024-42129 CVE-2024-43831                      CVE-2024-46772 CVE-2024-47753 CVE-2024-47754 CVE-2024-50056                      CVE-2024-50246 CVE-2024-53166 CVE-2024-57977 CVE-2024-58002                      CVE-2024-58005 CVE-2024-58079 CVE-2024-58090 CVE-2025-21702                      CVE-2025-21712 CVE-2025-21721 CVE-2025-21756 CVE-2025-21838                      CVE-2025-21844 CVE-2025-21846 CVE-2025-21848 CVE-2025-21855                      CVE-2025-21858 CVE-2025-21859 CVE-2025-21862 CVE-2025-21864                      CVE-2025-21865 CVE-2025-21866 CVE-2025-21867 CVE-2025-21871                      CVE-2025-21875 CVE-2025-21877 CVE-2025-21878 CVE-2025-21881                      CVE-2025-21887 CVE-2025-21891 CVE-2025-21898 CVE-2025-21899                      CVE-2025-21904 CVE-2025-21905 CVE-2025-21909 CVE-2025-21910                      CVE-2025-21912 CVE-2025-21913 CVE-2025-21914 CVE-2025-21916                      CVE-2025-21917 CVE-2025-21918 CVE-2025-21919 CVE-2025-21920                      CVE-2025-21922 CVE-2025-21924 CVE-2025-21925 CVE-2025-21926                      CVE-2025-21928 CVE-2025-21934 CVE-2025-21935 CVE-2025-21936                      CVE-2025-21937 CVE-2025-21938 CVE-2025-21941 CVE-2025-21943                      CVE-2025-21944 CVE-2025-21945 CVE-2025-21947 CVE-2025-21948                      CVE-2025-21950 CVE-2025-21951 CVE-2025-21956 CVE-2025-21957                      CVE-2025-21959 CVE-2025-21960 CVE-2025-21962 CVE-2025-21963                      CVE-2025-21964 CVE-2025-21968 CVE-2025-21970 CVE-2025-21971                      CVE-2025-21975 CVE-2025-21978 CVE-2025-21979 CVE-2025-21980                      CVE-2025-21981 CVE-2025-21986 CVE-2025-21991 CVE-2025-21992                      CVE-2025-21993 CVE-2025-21994 CVE-2025-21996 CVE-2025-21997                      CVE-2025-21999 CVE-2025-22004 CVE-2025-22005 CVE-2025-22007                      CVE-2025-22008 CVE-2025-22010 CVE-2025-22014 CVE-2025-22015

    Several vulnerabilities have been discovered in the Linux kernel that     may lead to a privilege escalation, denial of service or information     leaks.

    For the stable distribution (bookworm), these problems have been fixed in     version 6.1.133-1.

    We recommend that you upgrade your linux packages.

    For the detailed security status of linux please refer to its security     tracker page at:
    https://security-tracker.debian.org/tracker/linux

    Further information about Debian Security Advisories, how to apply     these updates to your system and frequently asked questions can be     found at: https://www.debian.org/security/

    Mailing list: debian-security-announce@lists.debian.org

Tenable has extracted the preceding description block directly from the Debian security advisory.

Note that Nessus has not tested for these issues but has instead relied only on the application's self-reported version number.

The remote Ubuntu 14.04 LTS / 16.04 LTS host has a package installed that is affected by multiple vulnerabilities as referenced in the USN-7429-1 advisory.

    Several security issues were discovered in the Linux kernel. An attacker could possibly use these to     compromise the system. This update corrects flaws in the following subsystems:

    - Drivers core;

    - HID subsystem;

    - Network drivers;

    - SCSI subsystem;

    - SuperH / SH-Mobile drivers;

    - File systems infrastructure;

    - Ext4 file system;

    - JFS file system;

    - Network file system (NFS) client;

    - Memory management;

    - Network namespace;

    - CAIF protocol;

    - Networking core;

    - HSR network protocol;

    - IPv4 networking;

    - IPv6 networking;

    - MAC80211 subsystem;

    - Network traffic control; (CVE-2025-21702, CVE-2024-53227, CVE-2024-46826, CVE-2024-49952,     CVE-2024-56600, CVE-2021-47235, CVE-2024-50265, CVE-2021-47119, CVE-2024-53165, CVE-2021-47483,     CVE-2024-50302, CVE-2024-56595, CVE-2024-50167, CVE-2024-56658, CVE-2024-49948, CVE-2024-26921,     CVE-2021-47602, CVE-2024-26863, CVE-2021-47320, CVE-2025-21700, CVE-2021-47122)

Tenable has extracted the preceding description block directly from the Ubuntu security advisory.

Note that Nessus has not tested for these issues but has instead relied only on the application's self-reported version number.

The remote Ubuntu 14.04 LTS / 16.04 LTS / 18.04 LTS host has a package installed that is affected by multiple vulnerabilities as referenced in the USN-7428-1 advisory.

    Demi Marie Obenour and Simon Gaiser discovered that several Xen para- virtualization device frontends did     not properly restrict the access rights of device backends. An attacker could possibly use a malicious Xen     backend to gain access to memory pages of a guest VM or cause a denial of service in the guest.
    (CVE-2022-23041)

    Several security issues were discovered in the Linux kernel. An attacker could possibly use these to     compromise the system. This update corrects flaws in the following subsystems:

    - HID subsystem;

    - Network drivers;

    - Mellanox network drivers;

    - SCSI subsystem;

    - SuperH / SH-Mobile drivers;

    - File systems infrastructure;

    - Ext4 file system;

    - JFS file system;

    - IP tunnels definitions;

    - Network namespace;

    - BPF subsystem;

    - Networking core;

    - HSR network protocol;

    - IPv4 networking;

    - IPv6 networking;

    - Network traffic control; (CVE-2024-56615, CVE-2024-56600, CVE-2025-21700, CVE-2024-56658,     CVE-2024-35960, CVE-2024-50265, CVE-2025-21702, CVE-2024-53227, CVE-2024-53165, CVE-2024-50167,     CVE-2024-26863, CVE-2024-35973, CVE-2024-46826, CVE-2021-47119, CVE-2024-50302, CVE-2024-49952,     CVE-2021-47101, CVE-2024-49948, CVE-2024-56595)

Tenable has extracted the preceding description block directly from the Ubuntu security advisory.

Note that Nessus has not tested for these issues but has instead relied only on the application's self-reported version number.

The version of kernel installed on the remote host is prior to 5.4.291-206.400. It is, therefore, affected by multiple vulnerabilities as referenced in the ALAS2KERNEL-5.4-2025-097 advisory.

    In the Linux kernel, the following vulnerability has been resolved:

    Squashfs: check the inode number is not the invalid value of zero (CVE-2024-26982)

    In the Linux kernel, the following vulnerability has been resolved:

    smb: client: fix UAF in smb2_reconnect_server() (CVE-2024-35870)

    In the Linux kernel, the following vulnerability has been resolved:

    pps: Fix a use-after-free (CVE-2024-57979)

    In the Linux kernel, the following vulnerability has been resolved:

    rtc: pcf85063: fix potential OOB write in PCF85063 NVMEM read (CVE-2024-58069)

    In the Linux kernel, the following vulnerability has been resolved:

    KVM: Explicitly verify target vCPU is online in kvm_get_vcpu() (CVE-2024-58083)

    In the Linux kernel, the following vulnerability has been resolved:

    sched: sch_cake: add bounds checks to host bulk flow fairness counts (CVE-2025-21647)

    In the Linux kernel, the following vulnerability has been resolved:

    net: sched: Disallow replacing of child qdisc from one parent to another (CVE-2025-21700)

    In the Linux kernel, the following vulnerability has been resolved:

    pfifo_tail_enqueue: Drop new packet when sch->limit == 0 (CVE-2025-21702)

    In the Linux kernel, the following vulnerability has been resolved:

    nilfs2: do not force clear folio if buffer is referenced (CVE-2025-21722)

    In the Linux kernel, the following vulnerability has been resolved:

    nbd: don't allow reconnect after disconnect (CVE-2025-21731)

    In the Linux kernel, the following vulnerability has been resolved:

    btrfs: fix use-after-free when attempting to join an aborted transaction (CVE-2025-21753)

    In the Linux kernel, the following vulnerability has been resolved:

    ndisc: extend RCU protection in ndisc_send_skb() (CVE-2025-21760)

    In the Linux kernel, the following vulnerability has been resolved:

    openvswitch: use RCU protection in ovs_vport_cmd_fill_info() (CVE-2025-21761)

    In the Linux kernel, the following vulnerability has been resolved:

    arp: use RCU protection in arp_xmit() (CVE-2025-21762)

    In the Linux kernel, the following vulnerability has been resolved:

    neighbour: use RCU protection in __neigh_notify() (CVE-2025-21763)

    In the Linux kernel, the following vulnerability has been resolved:

    ndisc: use RCU protection in ndisc_alloc_skb() (CVE-2025-21764)

    In the Linux kernel, the following vulnerability has been resolved:

    arm64: cacheinfo: Avoid out-of-bounds write to cacheinfo array (CVE-2025-21785)

    In the Linux kernel, the following vulnerability has been resolved:

    vrf: use RCU protection in l3mdev_l3_out() (CVE-2025-21791)

    In the Linux kernel, the following vulnerability has been resolved:

    nilfs2: protect access to buffers with no active references (CVE-2025-21811)

    In the Linux kernel, the following vulnerability has been resolved:

    geneve: Fix use-after-free in geneve_find_dev(). (CVE-2025-21858)

Tenable has extracted the preceding description block directly from the tested product security advisory.

Note that Nessus has not tested for these issues but has instead relied only on the application's self-reported version number.

It is, therefore, affected by multiple vulnerabilities as referenced in the ALAS2023-2025-901 advisory.

    In the Linux kernel, the following vulnerability has been resolved:

    smb: client: fix use-after-free of signing key (CVE-2024-53179)

    In the Linux kernel, the following vulnerability has been resolved:

    pfifo_tail_enqueue: Drop new packet when sch->limit == 0 (CVE-2025-21702)

    In the Linux kernel, the following vulnerability has been resolved:

    geneve: Fix use-after-free in geneve_find_dev(). (CVE-2025-21858)

    In the Linux kernel, the following vulnerability has been resolved:

    ovl: fix UAF in ovl_dentry_update_reval by moving dput() in ovl_link_up (CVE-2025-21887)

Tenable has extracted the preceding description block directly from the tested product security advisory.

Note that Nessus has not tested for these issues but has instead relied only on the application's self-reported version number.

The version of kernel installed on the remote host is prior to 4.14.355-275.603. It is, therefore, affected by multiple vulnerabilities as referenced in the ALAS2-2025-2800 advisory.

    In the Linux kernel, the following vulnerability has been resolved:

    smb: client: fix UAF in smb2_reconnect_server() (CVE-2024-35870)

    In the Linux kernel, the following vulnerability has been resolved:

    ext4: fix timer use-after-free on failed mount (CVE-2024-49960)

    In the Linux kernel, the following vulnerability has been resolved: HID: core: zero-initialize the report     buffer Since the report buffer is used by all kinds of drivers in various ways, let's zero-initialize it     during allocation to make sure that it can't be ever used to leak kernel memory via specially-crafted     report. (CVE-2024-50302)

    In the Linux kernel, the following vulnerability has been resolved:

    smb: client: fix use-after-free of signing key (CVE-2024-53179)

    In the Linux kernel, the following vulnerability has been resolved:

    pfifo_tail_enqueue: Drop new packet when sch->limit == 0 (CVE-2025-21702)

Tenable has extracted the preceding description block directly from the tested product security advisory.

Note that Nessus has not tested for these issues but has instead relied only on the application's self-reported version number.

An update of the linux package has been released.

The version of kernel installed on the remote host is prior to 5.10.234-225.917. It is, therefore, affected by multiple vulnerabilities as referenced in the ALAS2KERNEL-5.10-2025-085 advisory.

    Insufficient control flow management for the Intel(R) 82599 Ethernet Controllers and Adapters may allow an     authenticated user to potentially enable denial of service via local access. (CVE-2021-33061)

    In the Linux kernel, the following vulnerability has been resolved:

    KVM: x86: Acquire kvm->srcu when handling KVM_SET_VCPU_EVENTS (CVE-2024-46830)

    In the Linux kernel, the following vulnerability has been resolved:

    sched: sch_cake: add bounds checks to host bulk flow fairness counts (CVE-2025-21647)

    In the Linux kernel, the following vulnerability has been resolved:

    pfifo_tail_enqueue: Drop new packet when sch->limit == 0 (CVE-2025-21702)

    In the Linux kernel, the following vulnerability has been resolved:

    netem: Update sch->q.qlen before qdisc_tree_reduce_backlog() (CVE-2025-21703)

Tenable has extracted the preceding description block directly from the tested product security advisory.

Note that Nessus has not tested for these issues but has instead relied only on the application's self-reported version number.

The version of kernel installed on the remote host is prior to 5.15.178-120.187. It is, therefore, affected by multiple vulnerabilities as referenced in the ALAS2KERNEL-5.15-2025-067 advisory.

    In the Linux kernel, the following vulnerability has been resolved:

    smb: client: fix UAF in smb2_reconnect_server() (CVE-2024-35870)

    In the Linux kernel, the following vulnerability has been resolved:

    smb: client: fix use-after-free of signing key (CVE-2024-53179)

    In the Linux kernel, the following vulnerability has been resolved:

    sched: sch_cake: add bounds checks to host bulk flow fairness counts (CVE-2025-21647)

    In the Linux kernel, the following vulnerability has been resolved:

    pfifo_tail_enqueue: Drop new packet when sch->limit == 0 (CVE-2025-21702)

    In the Linux kernel, the following vulnerability has been resolved:

    netem: Update sch->q.qlen before qdisc_tree_reduce_backlog() (CVE-2025-21703)

Tenable has extracted the preceding description block directly from the tested product security advisory.

Note that Nessus has not tested for these issues but has instead relied only on the application's self-reported version number.

The version of kernel installed on the remote host is prior to 5.4.290-205.405. It is, therefore, affected by multiple vulnerabilities as referenced in the ALAS2KERNEL-5.4-2025-096 advisory.

    Insufficient control flow management for the Intel(R) 82599 Ethernet Controllers and Adapters may allow an     authenticated user to potentially enable denial of service via local access. (CVE-2021-33061)

    In the Linux kernel, the following vulnerability has been resolved:

    smb: client: fix UAF in smb2_reconnect_server() (CVE-2024-35870)

    In the Linux kernel, the following vulnerability has been resolved:

    smb: client: fix use-after-free of signing key (CVE-2024-53179)

    In the Linux kernel, the following vulnerability has been resolved:

    pfifo_tail_enqueue: Drop new packet when sch->limit == 0 (CVE-2025-21702)

    In the Linux kernel, the following vulnerability has been resolved:

    netem: Update sch->q.qlen before qdisc_tree_reduce_backlog() (CVE-2025-21703)

Tenable has extracted the preceding description block directly from the tested product security advisory.

Note that Nessus has not tested for these issues but has instead relied only on the application's self-reported version number.

The version of kernel installed on the remote host is prior to 4.14.355-195.603. It is, therefore, affected by multiple vulnerabilities as referenced in the ALAS-2025-1966 advisory.

    In the Linux kernel, the following vulnerability has been resolved:

    ext4: fix timer use-after-free on failed mount (CVE-2024-49960)

    In the Linux kernel, the following vulnerability has been resolved:

    smb: client: fix use-after-free of signing key (CVE-2024-53179)

    In the Linux kernel, the following vulnerability has been resolved:

    pfifo_tail_enqueue: Drop new packet when sch->limit == 0 (CVE-2025-21702)

Tenable has extracted the preceding description block directly from the tested product security advisory.

Note that Nessus has not tested for these issues but has instead relied only on the application's self-reported version number.

The Linux/Unix host has one or more packages installed that are impacted by a vulnerability without a vendor supplied patch available.

  - In the Linux kernel, the following vulnerability has been resolved: pfifo_tail_enqueue: Drop new packet     when sch->limit == 0 Expected behaviour: In case we reach scheduler's limit, pfifo_tail_enqueue() will     drop a packet in scheduler's queue and decrease scheduler's qlen by one. Then, pfifo_tail_enqueue()     enqueue new packet and increase scheduler's qlen by one. Finally, pfifo_tail_enqueue() return     `NET_XMIT_CN` status code. Weird behaviour: In case we set `sch->limit == 0` and trigger     pfifo_tail_enqueue() on a scheduler that has no packet, the 'drop a packet' step will do nothing. This     means the scheduler's qlen still has value equal 0. Then, we continue to enqueue new packet and increase     scheduler's qlen by one. In summary, we can leverage pfifo_tail_enqueue() to increase qlen by one and     return `NET_XMIT_CN` status code. The problem is: Let's say we have two qdiscs: Qdisc_A and Qdisc_B. -     Qdisc_A's type must have '->graft()' function to create parent/child relationship. Let's say Qdisc_A's     type is `hfsc`. Enqueue packet to this qdisc will trigger `hfsc_enqueue`. - Qdisc_B's type is     pfifo_head_drop. Enqueue packet to this qdisc will trigger `pfifo_tail_enqueue`. - Qdisc_B is configured     to have `sch->limit == 0`. - Qdisc_A is configured to route the enqueued's packet to Qdisc_B. Enqueue     packet through Qdisc_A will lead to: - hfsc_enqueue(Qdisc_A) -> pfifo_tail_enqueue(Qdisc_B) -     Qdisc_B->q.qlen += 1 - pfifo_tail_enqueue() return `NET_XMIT_CN` - hfsc_enqueue() check for     `NET_XMIT_SUCCESS` and see `NET_XMIT_CN` => hfsc_enqueue() don't increase qlen of Qdisc_A. The whole     process lead to a situation where Qdisc_A->q.qlen == 0 and Qdisc_B->q.qlen == 1. Replace 'hfsc' with other     type (for example: 'drr') still lead to the same problem. This violate the design where parent's qlen     should equal to the sum of its childrens'qlen. Bug impact: This issue can be used for user->kernel     privilege escalation when it is reachable. (CVE-2025-21702)

Note that Nessus relies on the presence of the package as reported by the vendor.

ID	Name	Product	Family	Severity
234309	Debian dsa-5900 : affs-modules-6.1.0-28-4kc-malta-di - security update	Nessus	Debian Local Security Checks	high
234107	Ubuntu 14.04 LTS / 16.04 LTS : Linux kernel vulnerabilities (USN-7429-1)	Nessus	Ubuntu Local Security Checks	high
234106	Ubuntu 14.04 LTS / 16.04 LTS / 18.04 LTS : Linux kernel vulnerabilities (USN-7428-1)	Nessus	Ubuntu Local Security Checks	high
233712	Amazon Linux 2 : kernel (ALASKERNEL-5.4-2025-097)	Nessus	Amazon Linux Local Security Checks	high
233394	Amazon Linux 2023 : bpftool, kernel, kernel-devel (ALAS2023-2025-901)	Nessus	Amazon Linux Local Security Checks	high
233381	Amazon Linux 2 : kernel (ALAS-2025-2800)	Nessus	Amazon Linux Local Security Checks	high
233213	Photon OS 4.0: Linux PHSA-2025-4.0-0771	Nessus	PhotonOS Local Security Checks	high
232919	Amazon Linux 2 : kernel (ALASKERNEL-5.10-2025-085)	Nessus	Amazon Linux Local Security Checks	medium
232918	Amazon Linux 2 : kernel (ALASKERNEL-5.15-2025-067)	Nessus	Amazon Linux Local Security Checks	high
232915	Amazon Linux 2 : kernel (ALASKERNEL-5.4-2025-096)	Nessus	Amazon Linux Local Security Checks	high
232891	Amazon Linux AMI : kernel (ALAS-2025-1966)	Nessus	Amazon Linux Local Security Checks	high
231558	Linux Distros Unpatched Vulnerability : CVE-2025-21702	Nessus	Misc.	medium

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CVE-2025-21702

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