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.

🗓️ 18 Aug 2020 07:00:00Reported by MicrosoftType

Bash flaw: saved user id not dropped when lowering the effective id, enabling privilege regain via enable builtins; zero effective user id binaries unaffected.

Reporter	Title	Published	Views	Family All 84
IBM Security Bulletins	Security Bulletin: Vulnerability in Bash (CVE-2019-18276) affects HMC	22 Nov 202106:16	–	ibm
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IBM Security Bulletins	Security Bulletin: Cloud Pak for Security uses packages that are vulnerable to several CVEs	19 Oct 202115:38	–	ibm
IBM Security Bulletins	Security Bulletin: IBM QRadar SIEM Application Framework Base Image is vulnerable to using components with Known Vulnerabilities	3 Dec 202118:52	–	ibm
0day.today	Bash 5.0 Patch 11 - SUID Priv Drop Exploit	29 Nov 201900:00	–	zdt
CBLMariner	CVE-2019-18276 affecting package bash 4.4.23-1	30 Nov 202019:30	–	cbl_mariner
Tenable Nessus	CentOS 8 : bash (CESA-2021:1679)	19 May 202100:00	–	nessus
Tenable Nessus	EulerOS 2.0 SP8 : bash (EulerOS-SA-2020-1140)	25 Feb 202000:00	–	nessus
Tenable Nessus	EulerOS 2.0 SP5 : bash (EulerOS-SA-2020-1303)	24 Mar 202000:00	–	nessus