# 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.

- **Severity:** Medium 6.2 (`CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 11 Mar 2026
- **Updated:** 15 Oct 2026
- **Also known as:** DEBIAN-CVE-2026-3904, GHSA-3584-5r39-4gm3

## 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 (Race Condition within a Thread)

## Which versions are affected by CVE-2026-3904?

It affects 1 product.


Products: 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

- [CVE-2026-5450](https://insights.sbomify.com/CVE-2026-5450/): scanf %mc off-by-one heap buffer overflow (critical 9.8)
- [CVE-2023-25139](https://insights.sbomify.com/CVE-2023-25139/): Memory corruption in n/a (critical 9.8)
- [CVE-1999-0199](https://insights.sbomify.com/CVE-1999-0199/): Other in n/a (critical 9.8)
- [CVE-2019-1010022](https://insights.sbomify.com/CVE-2019-1010022/): Security feature bypass in glibc (critical 9.8)
- [CVE-2005-3590](https://insights.sbomify.com/CVE-2005-3590/): Memory corruption in n/a (critical 9.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-3904 and fix it if it is affected.

What it is: 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.
Exploitation: There is no known exploitation of CVE-2026-3904 in the wild and no public exploit code.

Affected product: Gnu Glibc. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-3904/ (Markdown: https://insights.sbomify.com/CVE-2026-3904/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-3904
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-3904
- OSV: https://osv.dev/vulnerability/CVE-2026-3904

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-3904/
Summaries are generated and may contain mistakes; the official description above is the record.