CVE-2026-24061: GNU InetUtils telnetd authentication bypass via USER="-f root"

Exploited in the wild Critical 9.8 EPSS 99.0%

GNU InetUtils telnetd passes the client-supplied USER environment variable to /usr/bin/login unsanitised, so a client sending USER='-f root' (telnet -a) is logged in as root with no password. Any host running the InetUtils telnetd (packaged as inetutils-telnetd on Debian and Ubuntu) from version 1.9.3 through 2.7 is exposed. Disclosed on 20 January 2026; CISA added it to KEV on 26 January 2026.

CVE-2026-24061CVE identifier
9.8CVSS 3.1 base score (critical)
2026-01-26added to CISA's exploited list (US federal deadline 2026-02-16)
99.0%EPSS: chance of exploitation in the next 30 days (higher than 100% of CVEs)
2026-01-21published

What do these terms mean? CVE · CVSS score · exploited (KEV) · EPSS · backported fix · all terms

What to do now

Check whether you run the affected software and which version (commands below).
Install the fixed version for your system: see “Patch it” below.
Restart inetd (e.g. sudo systemctl restart inetutils-inetd) so new telnet sessions use the patched telnetd.
If you cannot patch today, apply the temporary mitigation below and patch as soon as possible.
Because this flaw is being exploited, also check the server for signs of compromise.

Affected and fixed versions

Affected:

GNU InetUtils 1.9.3 through 2.7

Am I affected?

dpkg -l inetutils-telnetd | grep ^ii
sudo ss -ltnp | grep ':23 '
grep -n telnet /etc/inetd.conf

Patch it

Use the commands for your system. Distribution packages often keep an older version number with the fix backported, so compare with the fixed package versions in the table below, not only with the upstream version.

Debian

sudo apt update
sudo apt install --only-upgrade inetutils-telnetd
# better: sudo apt purge inetutils-telnetd

Ubuntu

sudo apt update
sudo apt install --only-upgrade inetutils-telnetd
# better: sudo apt purge inetutils-telnetd

General update steps for every system are on the Linux and Unix & BSD pages; after updating, see which services to restart.

Fix status in Linux distributions

Release	Package	Status	Fixed version / advisory
Debian 12	`inetutils`	fixed	`2:2.4-2+deb12u2`
Debian 13	`inetutils`	fixed	`2:2.6-3+deb13u1`
Debian testing	`inetutils`	fixed	`2:2.7-2`
Debian 13 (trixie)	`inetutils`	fixed	`2:2.6-3+deb13u1 (DSA-6106-1)`
Debian 12 (bookworm)	`inetutils`	fixed	`2:2.4-2+deb12u2 (DSA-6106-1)`
Debian 11 (bullseye)	`inetutils`	fixed	`2:2.0-1+deb11u4 (DLA-4527-1)`
Ubuntu 24.04 LTS	`inetutils`	fixed	`2:2.5-3ubuntu4.1 (USN-7992-1)`
Ubuntu 22.04 LTS	`inetutils`	fixed	`2:2.2-2ubuntu0.2 (USN-7992-1)`
Ubuntu 20.04 LTS (ESM)	`inetutils`	fixed	`2:1.9.4-11ubuntu0.2+esm3 (USN-7992-2)`
Ubuntu 18.04 LTS (ESM)	`inetutils`	fixed	`2:1.9.4-3ubuntu0.1+esm4 (USN-7992-2)`

From the Debian security tracker, Ubuntu CVE tracker and Red Hat Security Data API, refreshed every few hours.

If you cannot patch yet

Do not run a telnet server at all; otherwise restrict TCP port 23 to trusted clients (InetUtils advisory).
Workaround: disable telnetd, or make it use a custom login(1) that does not accept the -f option.

CISA required action: Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.

This vulnerability could affect an open-source component, third-party library, protocol, or proprietary implementation that could be used by different products. For more information, please see: https://cgit.git.savannah.gnu.org/cgit/inetutils.git ; https://codeberg.org/inetutils/inetutils/commit/ccba9f748aa8d50a38d7748e2e60362edd6a32cc; https://codeberg.org/inetutils/inetutils/commit/fd702c02497b2f398e739e3119bed0b23dd7aa7b ; https://nvd.nist.gov/vuln/detail/CVE-2026-24061

Sources

Page generated automatically from official sources on 2026-11-03 18:05 UTC and reviewed by an editor. Always confirm with your vendor's advisory.