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CVE-2026-3904

MEDIUMCVSS 6.2/10EPSS 0.15%

Last modified

CVE-2026-3904 is a medium-severity vulnerability rated 6.2/10 on the CVSS scale. Calling NSS-backed functions that support caching via nscd may call the nscd client side code and in the GNU C Library version 2.36 under high load on x86_64 systems, the client may call memcmp on inputs that are concurrently modified by other processes or threads and crash. The nscd client in the GNU C Library uses the memcmp function with inputs that may be concurrently modified by another thread, potentially resulting in spurious cache misses, which in itself is not a security issue.  However in the GNU C Library version 2.36 an optimized implementation of memcmp was introduced for x86_64 which could crash when invoked with such undefined behaviour, turning this into a potential crash of the nscd client and the application that uses it. This implementation was backported to the 2.35 branch, making the nscd client in that branch vulnerable as well.  Subsequently, the fix for this issue was backported to all vulnerable branches in the GNU C Library repository. It is advised that distributions that may have cherry-picked the memcpy SSE2 optimization in their copy of the GNU C Library, also apply the fix to avoid the potential crash in the nscd client.. EPSS estimates a 0.15% chance of exploitation in the next 30 days.

Description

Calling NSS-backed functions that support caching via nscd may call the nscd client side code and in the GNU C Library version 2.36 under high load on x86_64 systems, the client may call memcmp on inputs that are concurrently modified by other processes or threads and crash. The nscd client in the GNU C Library uses the memcmp function with inputs that may be concurrently modified by another thread, potentially resulting in spurious cache misses, which in itself is not a security issue.  However in the GNU C Library version 2.36 an optimized implementation of memcmp was introduced for x86_64 which could crash when invoked with such undefined behaviour, turning this into a potential crash of the nscd client and the application that uses it. This implementation was backported to the 2.35 branch, making the nscd client in that branch vulnerable as well.  Subsequently, the fix for this issue was backported to all vulnerable branches in the GNU C Library repository. It is advised that distributions that may have cherry-picked the memcpy SSE2 optimization in their copy of the GNU C Library, also apply the fix to avoid the potential crash in the nscd client.

Metrics

CVSS 3.1
6.2/10

CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

EPSS Probability
0.15%

4.2th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

Affected Software

VendorProductVersions
GnuGlibc>= 2.35, < 2.37

References

Timeline

Published
Last Modified
Status
Analyzed

Frequently Asked Questions

What is CVE-2026-3904?
Calling NSS-backed functions that support caching via nscd may call the nscd client side code and in the GNU C Library version 2.36 under high load on x86_64 systems, the client may call memcmp on inputs that are concurrently modified by other processes or threads and crash. The nscd client in the GNU C Library uses the memcmp function with inputs that may be concurrently modified by another thread, potentially resulting in spurious cache misses, which in itself is not a security issue.  However in the GNU C Library version 2.36 an optimized implementation of memcmp was introduced for x86_64 which could crash when invoked with such undefined behaviour, turning this into a potential crash of the nscd client and the application that uses it. This implementation was backported to the 2.35 branch, making the nscd client in that branch vulnerable as well.  Subsequently, the fix for this issue was backported to all vulnerable branches in the GNU C Library repository. It is advised that distributions that may have cherry-picked the memcpy SSE2 optimization in their copy of the GNU C Library, also apply the fix to avoid the potential crash in the nscd client.
How severe is CVE-2026-3904?
CVE-2026-3904 has a CVSS score of 6.2/10 (MEDIUM severity). The EPSS model estimates a 0.15% probability of exploitation in the next 30 days.
How do I fix CVE-2026-3904?
Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2026-3904?

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Source: NVD / NIST