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CVE-2019-18276

Published: 28 November 2019

An issue was discovered in disable_priv_mode in shell.c in GNU Bash through 5.0 patch 11. By default, if Bash is run with its effective UID not equal to its real UID, it will drop privileges by setting its effective UID to its real UID. However, it does so incorrectly. On Linux and other systems that support "saved UID" functionality, the saved UID is not dropped. An attacker with command execution in the shell can use "enable -f" for runtime loading of a new builtin, which can be a shared object that calls setuid() and therefore regains privileges. However, binaries running with an effective UID of 0 are unaffected.

Notes

AuthorNote
sbeattie
This issue appears to only affect bash when bash is
setuid. Ubuntu does not ship with bash setuid, so this has minimal
impact for Ubuntu users. This is why we have rated the priority
for this issue 'low'.
reproducer steps in the suse bugzilla
Priority

Low

CVSS 3 base score: 7.8

Status

Package Release Status
bash
Launchpad, Ubuntu, Debian
bionic
Released (4.4.18-2ubuntu1.3)
disco Ignored
(reached end-of-life)
eoan Ignored
(reached end-of-life)
focal
Released (5.0-6ubuntu1.2)
groovy Ignored
(reached end-of-life)
hirsute Not vulnerable
(5.1-1ubuntu1)
impish Not vulnerable
(5.1-1ubuntu1)
jammy Not vulnerable
(5.1-1ubuntu1)
precise Ignored
(end of ESM support, was needed)
trusty
Released (4.3-7ubuntu1.8+esm2)
upstream
Released (5.1)
xenial
Released (4.3-14ubuntu1.4+esm1)
Patches:
upstream: https://git.savannah.gnu.org/cgit/bash.git/commit/?h=devel&id=951bdaad7a18cc0dc1036bba86b18b90874d39ff