Buffer overflow in At&t Bell Labs Unix
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 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.
Vulnerability class: Buffer Overflow
Published · last modified .
CVSS v3 metric
CVSS v3 base score 7.4 (High). Vector: CVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H.
EPSS exploit prediction
EPSS: 0.002 (7.7th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 8th percentile — 7.7% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.002 · newest: 0.002 · change: +0.000
Affected products
- At&t Bell Labs Unix — versions 4
- Opengroup Unix — versions 4
Weakness classification (CWE)
References
- sigma-star.at/blog/2025/12/unix-v4-buffer-overflow/ (Press/Media Coverage)
- www.tuhs.org/pipermail/tuhs/2026-January/032991.html (Mailing List, Issue Tracking)
- discuss.systems/@ricci/115747843169814700 (Issue Tracking)
- www.spinellis.gr/blog/20251223/ (Technical Description)
- af854a3a-2127-422b-91ae-364da2661108 (Issue Tracking, Mailing List)
- af854a3a-2127-422b-91ae-364da2661108 (Issue Tracking, Mailing List)
Frequently asked questions
- What is CVE-2025-71263?
- CVE-2025-71263 is a high-severity vulnerability in At&t Bell Labs Unix, classified under Buffer Copy without Checking Size of Input (Classic Buffer Overflow). CVSS score: 7.4/10. Published 2026-03-13.
- How severe is CVE-2025-71263?
- High severity. CVSS v3 base score is 7.4 out of 10.