Amazon Linux 2 : edk2 (ALAS-2024-2591)

critical Nessus Plugin ID 202987

Synopsis

The remote Amazon Linux 2 host is missing a security update.

Description

It is, therefore, affected by a vulnerability as referenced in the ALAS2-2024-2591 advisory.

Issue summary: Calling the OpenSSL API function SSL_select_next_proto with anempty supported client protocols buffer may cause a crash or memory contents tobe sent to the peer.

Impact summary: A buffer overread can have a range of potential consequencessuch as unexpected application beahviour or a crash. In particular this issuecould result in up to 255 bytes of arbitrary private data from memory being sentto the peer leading to a loss of confidentiality. However, only applicationsthat directly call the SSL_select_next_proto function with a 0 length list ofsupported client protocols are affected by this issue. This would normally neverbe a valid scenario and is typically not under attacker control but may occur byaccident in the case of a configuration or programming error in the callingapplication.

The OpenSSL API function SSL_select_next_proto is typically used by TLSapplications that support ALPN (Application Layer Protocol Negotiation) or NPN(Next Protocol Negotiation). NPN is older, was never standardised andis deprecated in favour of ALPN. We believe that ALPN is significantly morewidely deployed than NPN. The SSL_select_next_proto function accepts a list ofprotocols from the server and a list of protocols from the client and returnsthe first protocol that appears in the server list that also appears in theclient list. In the case of no overlap between the two lists it returns thefirst item in the client list. In either case it will signal whether an overlapbetween the two lists was found. In the case where SSL_select_next_proto iscalled with a zero length client list it fails to notice this condition andreturns the memory immediately following the client list pointer (and reportsthat there was no overlap in the lists).

This function is typically called from a server side application callback forALPN or a client side application callback for NPN. In the case of ALPN the listof protocols supplied by the client is guaranteed by libssl to never be zero inlength. The list of server protocols comes from the application and should nevernormally be expected to be of zero length. In this case if theSSL_select_next_proto function has been called as expected (with the listsupplied by the client passed in the client/client_len parameters), then theapplication will not be vulnerable to this issue. If the application hasaccidentally been configured with a zero length server list, and hasaccidentally passed that zero length server list in the client/client_lenparameters, and has additionally failed to correctly handle a no overlapresponse (which would normally result in a handshake failure in ALPN) then itwill be vulnerable to this problem.

In the case of NPN, the protocol permits the client to opportunistically selecta protocol when there is no overlap. OpenSSL returns the first client protocolin the no overlap case in support of this. The list of client protocols comesfrom the application and should never normally be expected to be of zero length.However if the SSL_select_next_proto function is accidentally called with aclient_len of 0 then an invalid memory pointer will be returned instead. If theapplication uses this output as the opportunistic protocol then the loss ofconfidentiality will occur.

This issue has been assessed as Low severity because applications are mostlikely to be vulnerable if they are using NPN instead of ALPN - but NPN is notwidely used. It also requires an application configuration or programming error.Finally, this issue would not typically be under attacker control making activeexploitation unlikely.

The FIPS modules in 3.3, 3.2, 3.1 and 3.0 are not affected by this issue.

Due to the low severity of this issue we are not issuing new releases ofOpenSSL at this time. The fix will be included in the next releases when theybecome available. (CVE-2024-5535)

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

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

Solution

Run 'yum update edk2' to update your system.

Plugin Details

Severity: Critical

ID: 202987

File Name: al2_ALAS-2024-2591.nasl

Version: 1.1

Type: local

Agent: unix

Family: Amazon Linux Local Security Checks

Published: 7/23/2024

Updated: 7/23/2024

Supported Sensors: Frictionless Assessment AWS, Frictionless Assessment Agent, Nessus Agent, Agentless Assessment, Nessus

Risk Information

VPR

Risk Factor: Medium

Score: 6.0

CVSS v2

Risk Factor: Medium

Base Score: 5.4

Temporal Score: 4

Vector: CVSS2#AV:N/AC:H/Au:N/C:N/I:N/A:C

CVSS Score Source: CVE-2024-5535

CVSS v3

Risk Factor: Critical

Base Score: 9.1

Temporal Score: 7.9

Vector: CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H

Temporal Vector: CVSS:3.0/E:U/RL:O/RC:C

Vulnerability Information

CPE: cpe:/o:amazon:linux:2, p-cpe:/a:amazon:linux:edk2-aarch64, p-cpe:/a:amazon:linux:edk2-debuginfo, p-cpe:/a:amazon:linux:edk2-ovmf, p-cpe:/a:amazon:linux:edk2-tools, p-cpe:/a:amazon:linux:edk2-tools-doc, p-cpe:/a:amazon:linux:edk2-tools-python

Required KB Items: Host/local_checks_enabled, Host/AmazonLinux/release, Host/AmazonLinux/rpm-list

Exploit Ease: No known exploits are available

Patch Publication Date: 7/18/2024

Vulnerability Publication Date: 6/26/2024

Reference Information

CVE: CVE-2024-5535

Detections

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