CVE-2026-3904: CWE-366 Race condition within a thread in The GNU C Library glibc
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.
AI Analysis
Technical Summary
The vulnerability (CVE-2026-3904) is a race condition in the nscd client code of the GNU C Library (glibc) versions 2.35 and 2.36 on x86_64 systems. The nscd client calls memcmp on data that may be concurrently modified by other threads, which is undefined behavior. An optimized memcmp implementation introduced in glibc 2.36 and backported to 2.35 can crash under these conditions, causing the nscd client and the application using it to crash. This issue does not lead to security breaches such as data leakage or privilege escalation but results in denial of service via application crashes. The fix has been backported to all vulnerable branches in the glibc repository, and distributions that cherry-picked the memcpy SSE2 optimization should apply the fix as well.
Potential Impact
The vulnerability can cause application crashes (denial of service) when the nscd client calls memcmp on concurrently modified inputs. There is no impact on confidentiality or integrity. No known exploits are reported in the wild.
Mitigation Recommendations
A fix has been backported to all vulnerable branches of the GNU C Library repository. It is recommended that distributions using glibc versions 2.35 and 2.36, especially those that have cherry-picked the memcpy SSE2 optimization, apply the official patches to prevent crashes. Patch status is not explicitly confirmed in the provided data; therefore, check the vendor advisory for the latest remediation guidance.
CVE-2026-3904: CWE-366 Race condition within a thread in The GNU C Library glibc
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.
CVSS v3.1
Score 6.2medium
Affected software
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Weaknesses
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
The vulnerability (CVE-2026-3904) is a race condition in the nscd client code of the GNU C Library (glibc) versions 2.35 and 2.36 on x86_64 systems. The nscd client calls memcmp on data that may be concurrently modified by other threads, which is undefined behavior. An optimized memcmp implementation introduced in glibc 2.36 and backported to 2.35 can crash under these conditions, causing the nscd client and the application using it to crash. This issue does not lead to security breaches such as data leakage or privilege escalation but results in denial of service via application crashes. The fix has been backported to all vulnerable branches in the glibc repository, and distributions that cherry-picked the memcpy SSE2 optimization should apply the fix as well.
Potential Impact
The vulnerability can cause application crashes (denial of service) when the nscd client calls memcmp on concurrently modified inputs. There is no impact on confidentiality or integrity. No known exploits are reported in the wild.
Mitigation Recommendations
A fix has been backported to all vulnerable branches of the GNU C Library repository. It is recommended that distributions using glibc versions 2.35 and 2.36, especially those that have cherry-picked the memcpy SSE2 optimization, apply the official patches to prevent crashes. Patch status is not explicitly confirmed in the provided data; therefore, check the vendor advisory for the latest remediation guidance.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- glibc
- Date Reserved
- 2026-03-10T19:52:49.054Z
- Cvss Version
- null
- State
- PUBLISHED
Threat ID: 69b171e72f860ef943cd65a0
Added to database: 03/11/2026, 13:45:11 UTC
Last enriched: 07/15/2026, 11:23:06 UTC
Last updated: 07/31/2026, 19:22:58 UTC
Views: 295
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