CVE-2021-4034
CVE-2021-4034 is a security flaw in Red Hat Polkit. Attackers can run their own code on Red Hat Polkit. The US Cybersecurity and Infrastructure Security Agency (CISA) added it to its catalog of flaws known to be used in attacks on 27 Jun 2022, and says ransomware gangs have used it.[1]
Red Hat Polkit is business software or equipment. Most families won’t have it, but attackers break into it to get inside companies, and from there to what those companies hold about their customers, patients and staff. Red Hat has published a fix or advice.
Description
CISA calls it an out-of-bounds read and write in Red Hat Polkit. In its words: “The Red Hat polkit pkexec utility contains an out-of-bounds read and write vulnerability that allows for privilege escalation with administrative rights.”[1]
The CVE record adds: “A local privilege escalation vulnerability was found on polkit's pkexec utility. The pkexec application is a setuid tool designed to allow unprivileged users to run commands as privileged users according predefined policies. The current version of pkexec doesn't handle the calling parameters count correctly and ends trying to execute environment variables as commands. An attacker can leverage this by crafting environment variables in such a way it'll induce pkexec to execute arbitrary code. When successfully executed the attack can cause a local privilege escalation given unprivileged users administrative rights on the target machine.”[2]
The underlying weakness is out-of-bounds write (CWE-787), in MITRE’s list of common software weaknesses.
It scores 7.8 out of 10 on the Common Vulnerability Scoring System, which rates it high, scored by NVD using CVSS 3.1.[2]
Affected versions
NVD’s record doesn’t list version ranges for it; Red Hat’s advisory has them[3]. CISA names the product as Red Hat Polkit.
Most families won’t have Red Hat Polkit; it’s for whoever looks after IT at work.
Exploitation
CISA added it to its catalog of known exploited vulnerabilities on 27 Jun 2022, 150 days after it was made public. CISA lists a flaw only when it has reliable evidence of it being exploited, and gave US federal agencies until 18 Jul 2022 to fix it.[1] CISA says ransomware gangs have used it.
FIRST’s Exploit Prediction Scoring System, which estimates how likely a flaw is to be used in attacks in the next 30 days from what it sees across the internet, puts it at 95%. That’s in the top 1% of the flaws it scores.[4]
CISA assesses it as not automatable: each attack takes some work.
CISA doesn’t say who was attacked, or how.
Fix
Red Hat has published a fix or advice.[3] CISA’s required action: “Apply updates per vendor instructions.”[1]
- Check whether you use it.Red Hat Polkit is business software or equipment, so most families won’t have it. If you run a business, or work from home on company equipment, ask whoever looks after your IT.
- Send this page to your IT person.Ask them to confirm it’s fixed, or not in use. CISA gave US government agencies until 18 Jul 2022 to fix it.
- If it can’t be fixed, take it offline.CISA’s advice when there’s no fix is to stop using the product, or take it off the internet, until there is one.
You can’t fix someone else’s server, but you can watch for what follows a break-in like this: a breach notice, a password reset you didn’t ask for, or a scam message that knows things it shouldn’t. HARD watches for those for you and your family.
Timeline
| Date | Event |
|---|---|
| The flaw is made public in the National Vulnerability Database, with a severity score of 7.8.[2] | |
| CISA adds it to its catalog of flaws known to be used in attacks, noting that ransomware gangs have used it.[1] | |
| CISA’s deadline for US government agencies to fix it.[1] | |
| FIRST puts the odds of it being used in attacks in the next 30 days at 95%.[4] |
See also
Other Red Hat Polkit flaws
- CVE-2021-3560: incorrect authorization ·
Other Red Hat flaws
- CVE-2015-5287, Red Hat Automatic Bug Reporting Tool: privilege escalation ·
- CVE-2015-3246, Red Hat Libuser: race condition ·
- CVE-2018-14667, Red Hat JBoss RichFaces Framework: expression language injection ·
- CVE-2010-1428, Red Hat JBoss: information disclosure ·
- CVE-2010-0738, Red Hat JBoss: authentication bypass ·
Other out-of-bounds write flaws
- CVE-2026-86950, Apple devices: out-of-bounds write ·
- CVE-2026-53266, Linux Kernel: out-of-bounds write ·
- CVE-2026-87491, Chrome and other Chromium browsers: out of bounds write ·
- CVE-2026-53362, Linux Kernel: unspecified ·
- CVE-2022-0995, Linux Kernel: out-of-bounds write ·
Added the same day
- CVE-2022-29499, Mitel MiVoice Connect: data validation ·
- CVE-2021-30983, Apple iOS and iPadOS: buffer overflow ·
- CVE-2021-30533, Chrome and other Chromium browsers: security bypass ·
- CVE-2020-9907, Apple devices: memory corruption ·
- CVE-2020-3837, Apple devices: memory corruption ·
Every Red Hat flaw on CISA’s list · Everything added in June 2022
References
- ^ Cybersecurity and Infrastructure Security Agency. “Red Hat Polkit Out-of-Bounds Read and Write Vulnerability”. Known Exploited Vulnerabilities Catalog, added 27 Jun 2022.
- ^ National Institute of Standards and Technology. “CVE-2021-4034 Detail”. National Vulnerability Database, published 28 Jan 2022.
- ^ Red Hat. Advisories and fixes: access.redhat.com, bugzilla.redhat.com, gitlab.freedesktop.org, oracle.com.
- ^ FIRST. “Exploit Prediction Scoring System”. EPSS 0.949, percentile 99.9, 31 Oct 2026.
- CVE Program. “CVE-2021-4034”. The official CVE record.
This article is built from CISA’s catalog (version 2026.10.30), NVD’s record and FIRST’s scores, kept in HARD’s database and checked every morning. The plain English is HARD’s.