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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 Severity Score

7.8

Score breakdown

Status

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

Severity score breakdown

Parameter Value
Base score 7.8
Attack vector Local
Attack complexity Low
Privileges required Low
User interaction None
Scope Unchanged
Confidentiality High
Integrity impact High
Availability impact High
Vector CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H