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CVE-2024-2961: glibc

Title

CVE-2024-2961: glibc: Out of bounds write in iconv may lead to remote code execution

Summary

As described by Red Hat:

An out-of-bounds write flaw was found in the ISO-2022-CN-EXT plugin for glibc's iconv library. When converting from UCS4 charset, adding certain escape charterers is required to indicate where the charset was changed to the library. During this process, iconv improperly checks the boundaries of internal buffers, leading to a buffer overflow, which allows writing up to 3 bytes outside the desired memory location. This issue may allow an attacker to craft a malicious characters sequence that will trigger the out-of-bounds write and perform remote code execution, presenting a high impact to the Integrity, Confidentiality, and Availability triad.

and as further discussed on oss-security:

On PHP [this glibc bug led] to amazing results: a new exploitation technique that affects the whole PHP ecosystem.

Public disclosure date: April 17, 2024

EL9

  • Fixed in version: 2.34-83.12.el9_3.security.0.5 available April 18, 2024

EL8

  • Fixed in version: 2.28-236.el8_9.13 available May 7, 2024
  • Errata: RLSA-2024:2722 issued May 9, 2024

Mitigation

Support for the ISO-2022-CN-EXT character set can be excluded from glibc's iconv(3) by editing /usr/lib64/gconv/gconv-modules.d/gconv-modules-extra.conf to comment out the below 3 lines at line 1254 (same line number in EL9 and EL8) and then regenerating the cache file:

alias  ISO2022CNEXT//          ISO-2022-CN-EXT//
module ISO-2022-CN-EXT//       INTERNAL                ISO-2022-CN-EXT 1
module INTERNAL                ISO-2022-CN-EXT//       ISO-2022-CN-EXT 1

These two steps can be accomplished by running the below commands as root:

sed -i -r 's/^(.*ISO-2022-CN-EXT.*)$/#\1/' /usr/lib64/gconv/gconv-modules.d/gconv-modules-extra.conf
iconvconfig

To make sure this has worked as intended, we also recommend that you run iconv -l | grep ISO-2022-CN-EXT before and after the above procedure. It should list the ISO-2022-CN-EXT character set before the procedure, but produce empty output afterwards.

Making the fix or mitigation effective

After installing a fixed version of glibc or/and applying the mitigation, you'll need to restart any long-running processes for which the bug matters (such as PHP-FPM).