The __block_prepare_write function in fs/buffer.c for Linux kernel 2.6.x before 2.6.13 does not properly clear buffers during certain error conditions, which allows local users to read portions of files that have been unlinked.

From Red Hat Security Advisory 2007:0014 :

Updated kernel packages that fix several security issues in the Red Hat Enterprise Linux 4 kernel are now available.

This security advisory has been rated as having important security impact by the Red Hat Security Response Team.

The Linux kernel handles the basic functions of the operating system.

These new kernel packages contain fixes for the security issues described below :

* a flaw in the get_fdb_entries function of the network bridging support that allowed a local user to cause a denial of service (crash) or allow a potential privilege escalation (CVE-2006-5751, Important)

* an information leak in the _block_prepare_write function that allowed a local user to read kernel memory (CVE-2006-4813, Important)

* an information leak in the copy_from_user() implementation on s390 and s390x platforms that allowed a local user to read kernel memory (CVE-2006-5174, Important)

* a flaw in the handling of /proc/net/ip6_flowlabel that allowed a local user to cause a denial of service (infinite loop) (CVE-2006-5619, Important)

* a flaw in the AIO handling that allowed a local user to cause a denial of service (panic) (CVE-2006-5754, Important)

* a race condition in the mincore system core that allowed a local user to cause a denial of service (system hang) (CVE-2006-4814, Moderate)

* a flaw in the ELF handling on ia64 and sparc architectures which triggered a cross-region memory mapping and allowed a local user to cause a denial of service (CVE-2006-4538, Moderate)

* a flaw in the dev_queue_xmit function of the network subsystem that allowed a local user to cause a denial of service (data corruption) (CVE-2006-6535, Moderate)

* a flaw in the handling of CAPI messages over Bluetooth that allowed a remote system to cause a denial of service or potential code execution. This flaw is only exploitable if a privileged user establishes a connection to a malicious remote device (CVE-2006-6106, Moderate)

* a flaw in the listxattr system call that allowed a local user to cause a denial of service (data corruption) or potential privilege escalation. To successfully exploit this flaw the existence of a bad inode is required first (CVE-2006-5753, Moderate)

* a flaw in the __find_get_block_slow function that allowed a local privileged user to cause a denial of service (CVE-2006-5757, Low)

* various flaws in the supported filesystems that allowed a local privileged user to cause a denial of service (CVE-2006-5823, CVE-2006-6053, CVE-2006-6054, CVE-2006-6056, Low)

In addition to the security issues described above, fixes for the following bugs were included :

* initialization error of the tg3 driver with some BCM5703x network card

* a memory leak in the audit subsystem

* x86_64 nmi watchdog timeout is too short

* ext2/3 directory reads fail intermittently

Red Hat would like to thank Dmitriy Monakhov and Kostantin Khorenko for reporting issues fixed in this erratum.

All Red Hat Enterprise Linux 4 users are advised to upgrade their kernels to the packages associated with their machine architecture and configurations as listed in this erratum.

Updated kernel packages that fix several security issues in the Red Hat Enterprise Linux 4 kernel are now available.

This security advisory has been rated as having important security impact by the Red Hat Security Response Team.

The Linux kernel handles the basic functions of the operating system.

These new kernel packages contain fixes for the security issues described below :

* a flaw in the get_fdb_entries function of the network bridging support that allowed a local user to cause a denial of service (crash) or allow a potential privilege escalation (CVE-2006-5751, Important)

* an information leak in the _block_prepare_write function that allowed a local user to read kernel memory (CVE-2006-4813, Important)

* an information leak in the copy_from_user() implementation on s390 and s390x platforms that allowed a local user to read kernel memory (CVE-2006-5174, Important)

* a flaw in the handling of /proc/net/ip6_flowlabel that allowed a local user to cause a denial of service (infinite loop) (CVE-2006-5619, Important)

* a flaw in the AIO handling that allowed a local user to cause a denial of service (panic) (CVE-2006-5754, Important)

* a race condition in the mincore system core that allowed a local user to cause a denial of service (system hang) (CVE-2006-4814, Moderate)

* a flaw in the ELF handling on ia64 and sparc architectures which triggered a cross-region memory mapping and allowed a local user to cause a denial of service (CVE-2006-4538, Moderate)

* a flaw in the dev_queue_xmit function of the network subsystem that allowed a local user to cause a denial of service (data corruption) (CVE-2006-6535, Moderate)

* a flaw in the handling of CAPI messages over Bluetooth that allowed a remote system to cause a denial of service or potential code execution. This flaw is only exploitable if a privileged user establishes a connection to a malicious remote device (CVE-2006-6106, Moderate)

* a flaw in the listxattr system call that allowed a local user to cause a denial of service (data corruption) or potential privilege escalation. To successfully exploit this flaw the existence of a bad inode is required first (CVE-2006-5753, Moderate)

* a flaw in the __find_get_block_slow function that allowed a local privileged user to cause a denial of service (CVE-2006-5757, Low)

* various flaws in the supported filesystems that allowed a local privileged user to cause a denial of service (CVE-2006-5823, CVE-2006-6053, CVE-2006-6054, CVE-2006-6056, Low)

In addition to the security issues described above, fixes for the following bugs were included :

* initialization error of the tg3 driver with some BCM5703x network card

* a memory leak in the audit subsystem

* x86_64 nmi watchdog timeout is too short

* ext2/3 directory reads fail intermittently

Red Hat would like to thank Dmitriy Monakhov and Kostantin Khorenko for reporting issues fixed in this erratum.

All Red Hat Enterprise Linux 4 users are advised to upgrade their kernels to the packages associated with their machine architecture and configurations as listed in this erratum.

Mark Dowd discovered that the netfilter iptables module did not correcly handle fragmented packets. By sending specially crafted packets, a remote attacker could exploit this to bypass firewall rules. This has only be fixed for Ubuntu 6.10; the corresponding fix for Ubuntu 5.10 and 6.06 will follow soon. (CVE-2006-4572)

Dmitriy Monakhov discovered an information leak in the
__block_prepare_write() function. During error recovery, this function did not properly clear memory buffers which could allow local users to read portions of unlinked files. This only affects Ubuntu 5.10.
(CVE-2006-4813)

ADLab Venustech Info Ltd discovered that the ATM network driver referenced an already released pointer in some circumstances. By sending specially crafted packets to a host over ATM, a remote attacker could exploit this to crash that host. This does not affect Ubuntu 6.10. (CVE-2006-4997)

Matthias Andree discovered that the NFS locking management daemon (lockd) did not correctly handle mixing of 'lock' and 'nolock' option mounts on the same client. A remote attacker could exploit this to crash lockd and thus rendering the NFS imports inaccessible. This only affects Ubuntu 5.10. (CVE-2006-5158)

The task switching code did not save and restore EFLAGS of processes.
By starting a specially crafted executable, a local attacker could exploit this to eventually crash many other running processes. This does not affect Ubuntu 6.10. (CVE-2006-5173)

James Morris discovered that the ip6fl_get_n() function incorrectly handled flow labels. A local attacker could exploit this to crash the kernel. (CVE-2006-5619)

Fabio Massimo Di Nitto discovered that the sys_get_robust_list and sys_set_robust_list system calls lacked proper lock handling on the powerpc platform. A local attacker could exploit this to create unkillable processes, drain all available CPU/memory, and render the machine unrebootable. This only affects Ubuntu 6.10. (CVE-2006-5648)

Fabio Massimo Di Nitto discovered a flaw in the alignment check exception handling on the powerpc platform. A local attacker could exploit this to cause a kernel panic and crash the machine.
(CVE-2006-5649)

Certain corrupted squashfs file system images caused a memory allocation to be freed twice. By mounting a specially crafted squashfs file system, a local attacker could exploit this to crash the kernel.
This does not affect Ubuntu 5.10. (CVE-2006-5701)

An integer overflow was found in the get_fdb_entries() function of the network bridging code. By executing a specially crafted ioctl, a local attacker could exploit this to execute arbitrary code with root privileges. (CVE-2006-5751).

Note that Tenable Network Security has extracted the preceding description block directly from the Ubuntu security advisory. Tenable has attempted to automatically clean and format it as much as possible without introducing additional issues.

Some vulnerabilities were discovered and corrected in the Linux 2.6 kernel :

The __block_prepate_write function in the 2.6 kernel before 2.6.13 does not properly clear buffers during certain error conditions, which allows users to read portions of files that have been unlinked (CVE-2006-4813).

The clip_mkip function of the ATM subsystem in the 2.6 kernel allows remote attackers to dause a DoS (panic) via unknown vectors that cause the ATM subsystem to access the memory of socket buffers after they are freed (CVE-2006-4997).

The NFS lockd in the 2.6 kernel before 2.6.16 allows remote attackers to cause a DoS (process crash) and deny access to NFS exports via unspecified vectors that trigger a kernel oops and a deadlock (CVE-2006-5158).

The seqfile handling in the 2.6 kernel up to 2.6.18 allows local users to cause a DoS (hang or oops) via unspecified manipulations that trigger an infinite loop while searching for flowlabels (CVE-2006-5619).

A missing call to init_timer() in the isdn_ppp code of the Linux kernel can allow remote attackers to send a special kind of PPP pakcet which may trigger a kernel oops (CVE-2006-5749).

An integer overflow in the 2.6 kernel prior to 2.6.18.4 could allow a local user to execute arbitrary code via a large maxnum value in an ioctl request (CVE-2006-5751).

A race condition in the ISO9660 filesystem handling could allow a local user to cause a DoS (infinite loop) by mounting a crafted ISO9660 filesystem containing malformed data structures (CVE-2006-5757).

A vulnerability in the bluetooth support could allow for overwriting internal CMTP and CAPI data structures via malformed packets (CVE-2006-6106).

The provided packages are patched to fix these vulnerabilities. All users are encouraged to upgrade to these updated kernels immediately and reboot to effect the fixes.

In addition to these security fixes, other fixes have been included such as :

  - __bread oops fix

  - added e1000_ng (nineveh support)

  - added sata_svw (Broadcom SATA support)

  - added Marvell PATA chipset support

  - disabled mmconf on some broken hardware/BIOSes

  - use GENERICARCH and enable bigsmp apic model for tulsa     machines

To update your kernel, please follow the directions located at :

http://www.mandriva.com/en/security/kernelupdate

Several local and remote vulnerabilities have been discovered in the Linux kernel that may lead to a denial of service or the execution of arbitrary code. The Common Vulnerabilities and Exposures project identifies the following problems :

  - CVE-2006-3741     Stephane Eranian discovered a local DoS (Denial of     Service) vulnerability on the ia64 architecture. A local     user could exhaust the available file descriptors by     exploiting a counting error in the permonctl() system     call.

  - CVE-2006-4538     Kirill Korotaev reported a local DoS (Denial of Service)     vulnerability on the ia64 and sparc architectures. A     user could cause the system to crash by executing a     malformed ELF binary due to insufficient verification of     the memory layout.

  - CVE-2006-4813     Dmitriy Monakhov reported a potential memory leak in the
    __block_prepare_write function. __block_prepare_write     does not properly sanitize kernel buffers during error     recovery, which could be exploited by local users to     gain access to sensitive kernel memory.

  - CVE-2006-4997     ADLab Venustech Info Ltd reported a potential remote DoS     (Denial of Service) vulnerability in the IP over ATM     subsystem. A remote system could cause the system to     crash by sending specially crafted packets that would     trigger an attempt to free an already-freed pointer     resulting in a system crash.

  - CVE-2006-5174     Martin Schwidefsky reported a potential leak of     sensitive information on s390 systems. The     copy_from_user function did not clear the remaining     bytes of the kernel buffer after receiving a fault on     the userspace address, resulting in a leak of     uninitialized kernel memory. A local user could exploit     this by appending to a file from a bad address.

  - CVE-2006-5619     James Morris reported a potential local DoS (Denial of     Service) vulnerability that could be used to hang or     oops a system. The seqfile handling for     /proc/net/ip6_flowlabel has a flaw that can be exploited     to cause an infinite loop by reading this file after     creating a flowlabel.

  - CVE-2006-5649     Fabio Massimo Di Nitto reported a potential remote DoS     (Denial of Service) vulnerability on powerpc systems.
    The alignment exception only checked the exception table     for -EFAULT, not for other errors. This can be exploited     by a local user to cause a system crash (panic).

  - CVE-2006-5751     Eugene Teo reported a vulnerability in the     get_fdb_entries function that could potentially be     exploited to allow arbitrary code execution with     escalated privileges.

  - CVE-2006-5871     Bill Allombert reported that various mount options are     ignored by smbfs when UNIX extensions are enabled. This     includes the uid, gid and mode options. Client systems     would silently use the server-provided settings instead     of honoring these options, changing the security model.
    This update includes a fix from Haroldo Gamal that     forces the kernel to honor these mount options. Note     that, since the current versions of smbmount always pass     values for these options to the kernel, it is not     currently possible to activate unix extensions by     omitting mount options. However, this behavior is     currently consistent with the current behavior of the     next Debian release, 'etch'.

The remote CentOS system is missing a security update which has been documented in Red Hat advisory RHSA-2007-0014.

ID	Name	Product	Family	Severity
67438	Oracle Linux 4 : kernel (ELSA-2007-0014)	Nessus	Oracle Linux Local Security Checks	high
36838	CentOS 4 : kernel (CESA-2007:0014)	Nessus	CentOS Local Security Checks	high
27981	Ubuntu 5.10 / 6.06 LTS / 6.10 : linux-source-2.6.12/-2.6.15/-2.6.17 vulnerabilities (USN-395-1)	Nessus	Ubuntu Local Security Checks	high
24628	Mandrake Linux Security Advisory : kernel (MDKSA-2007:012)	Nessus	Mandriva Local Security Checks	high
24315	RHEL 4 : kernel (RHSA-2007:0014)	Nessus	Red Hat Local Security Checks	high
23846	Debian DSA-1233-1 : kernel-source-2.6.8 - several vulnerabilities	Nessus	Debian Local Security Checks	high
801424	CentOS RHSA-2007-0014 Security Check	Log Correlation Engine	Generic	high

Detections

Analytics

CVE-2006-4813

medium

Tenable Plugins

high

high

high

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high

high