CVE-2025-71263: AT&T Bell Labs UNIX · Classic Buffer Overflow
Affects AT&T Bell Labs UNIXSource CVE Database V5
Not known to be exploited · CVSS 7.4 High · end of life, no fix coming : replace or isolate AT&T Bell Labs UNIX; no fix will be released.
Data as of 30 Oct 2026, 06:59 UTC
- EPSS
- 0.1% chance of exploitation in 30 days – higher than 8% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
- Patch
- None coming – the product is end of life
CVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:HExploitation evidence
Disclosed: evidence found.
CVE published 13 Mar 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors
A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 29 Oct 2026.
What to do
No fix will be released: AT&T Bell Labs UNIX is end of life. Replace it, or isolate it from untrusted networks until you can.
Affected software
| Product | Affected | Fixed in |
|---|---|---|
| AT&T Bell LabsUNIX | Affected
| Fixed in– |
AI-suggested
Given the unsupported status of UNIX v4, the primary mitigation is to phase out or isolate affected systems from production and network environments. If continued use is necessary, restrict local user access to trusted personnel only and monitor for unusual activity. Employ system-level controls such as mandatory access controls (MAC) or sandboxing to limit the impact of potential exploitation. Since no official patches exist, consider applying manual source code audits and recompilation with added bounds checking if source code is available. Use virtualization or containerization to encapsulate legacy environments, reducing exposure. Maintain strict physical security and access logging to detect unauthorized local access attempts. Document and segregate legacy systems to prevent cross-contamination with modern infrastructure.
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.
References
- sigma-star.at/blog/2025/12/unix-v4-buffer-overflow/ (opens in a new tab)
- tuhs.org/pipermail/tuhs/2026-January/032991.html (opens in a new tab)
- discuss.systems/@ricci/115747843169814700 (opens in a new tab)
- spinellis.gr/blog/20251223/ (opens in a new tab)
- openwall.com/lists/oss-security/2026/03/20/6 (opens in a new tab)
- openwall.com/lists/oss-security/2026/03/21/4 (opens in a new tab)