CVE-2026-3904 Race condition in glibc
A race condition in the glibc nscd client can cause application crashes on x86_64 systems under high load due to unsafe concurrent memory access.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-3904?
CVE-2026-3904 is a medium-severity vulnerability in Gnu Glibc, published on 11 Mar 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official 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.
Weakness: CWE-366
Which versions are affected by CVE-2026-3904?
It affects 1 product.
Products include Gnu Glibc.
How do I fix CVE-2026-3904?
Apply the vendor's patch.
Is CVE-2026-3904 being exploited?
There is no known exploitation of CVE-2026-3904 in the wild and no public exploit code.
Other vulnerabilities in Gnu Glibc
Sources
Also known as DEBIAN-CVE-2026-3904, GHSA-3584-5r39-4gm3.