Description
The overlayfs implementation in the linux kernel did not properly validate with respect to user namespaces the setting of file capabilities on files in an underlying file system. Due to the combination of unprivileged user namespaces along with a patch carried in the Ubuntu kernel to allow unprivileged overlay mounts, an attacker could use this to gain elevated privileges.
Affected products
| Vendor | Product | Affected | Fixed |
|---|---|---|---|
| Ubuntu | linux kernel | 5.8 kernel – < 5.8.0-50.56, 5.4 kernel – < 5.4.0-72.80, 4.15 kernel – < 4.15.0-142.146, 4.4 kernel – < 4.4.0-209.241 | 5.8.0-50.56 |
Fixed in Linux distributions
Distributions backport fixes, so the version that fixes this vulnerability differs per release — upgrade to at least the version shown. From the distributions' security trackers and advisories.
Debian
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian 14 | linux | 5.10.38-1 | — |
| Debian 13 | linux | 5.10.38-1 | — |
| Debian 12 | linux | 5.10.38-1 | — |
Ubuntu
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu 24.04 LTS | linux-raspi-realtime | No fix yet | — |
| Ubuntu 22.04 LTS | linux-realtime +1 | No fix yet | — |
| Ubuntu 20.04 LTS | linux | 5.4.0-72.80 | USN-4917-1 |
| Ubuntu 20.04 LTS | linux-aws | 5.4.0-1045.47 | USN-4917-1 |
| Ubuntu 20.04 LTS | linux-azure | 5.4.0-1046.48 | USN-4917-1 |
| Ubuntu 20.04 LTS | linux-gcp | 5.4.0-1042.45 | USN-4917-1 |
| Ubuntu 20.04 LTS | linux-gke | 5.4.0-1042.44 | — |
| Ubuntu 20.04 LTS | linux-gkeop | 5.4.0-1014.15 | USN-4917-1 |
| Ubuntu 20.04 LTS | linux-hwe-5.8 | 5.8.0-50.56~20.04.1 | USN-4917-1 |
| Ubuntu 20.04 LTS | linux-kvm | 5.4.0-1038.39 | USN-4917-1 |
| Ubuntu 20.04 LTS | linux-oem-5.10 | 5.10.0-1022.23 | USN-4917-1 |
| Ubuntu 20.04 LTS | linux-oem-5.6 | 5.6.0-1054.58 | USN-4915-1 |
| Ubuntu 20.04 LTS | linux-oracle | 5.4.0-1043.46 | USN-4917-1 |
| Ubuntu 20.04 LTS | linux-raspi | 5.4.0-1034.37 | USN-4917-1 |
| Ubuntu 20.04 LTS | linux-riscv +1 | No fix yet | — |
| Ubuntu 20.04 LTS | linux-riscv-5.8 | 5.8.0-22.24~20.04.1 | — |
| Ubuntu 18.04 LTS | linux | 4.15.0-142.146 | USN-4916-1 |
| Ubuntu 18.04 LTS | linux-aws | 4.15.0-1099.106 | USN-4916-1 |
| Ubuntu 18.04 LTS | linux-aws-5.4 | 5.4.0-1045.47~18.04.1 | USN-4917-1 |
| Ubuntu 18.04 LTS | linux-azure-4.15 | 4.15.0-1113.126 | USN-4916-1 |
| Ubuntu 18.04 LTS | linux-azure-5.4 | 5.4.0-1046.48~18.04.1 | USN-4917-1 |
| Ubuntu 18.04 LTS | linux-dell300x | 4.15.0-1017.21 | USN-4916-1 |
| Ubuntu 18.04 LTS | linux-gcp +12 | No fix yet | — |
| Ubuntu 18.04 LTS | linux-gcp-4.15 | 4.15.0-1098.111 | USN-4916-1 |
| Ubuntu 18.04 LTS | linux-gcp-5.4 | 5.4.0-1042.45~18.04.1 | USN-4917-1 |
| Ubuntu 18.04 LTS | linux-gke-5.3 | 5.3.0-1042.45 | USN-4917-1 |
| Ubuntu 18.04 LTS | linux-gke-5.4 | 5.4.0-1042.44~18.04.1 | USN-4917-1 |
| Ubuntu 18.04 LTS | linux-gkeop-5.4 | 5.4.0-1014.15~18.04.1 | USN-4917-1 |
| Ubuntu 18.04 LTS | linux-hwe | 5.3.0-73.69 | USN-4917-1 |
| Ubuntu 18.04 LTS | linux-hwe-5.4 | 5.4.0-72.80~18.04.1 | USN-4917-1 |
| Ubuntu 18.04 LTS | linux-kvm | 4.15.0-1090.92 | USN-4916-1 |
| Ubuntu 18.04 LTS | linux-oracle | 4.15.0-1070.78 | USN-4916-1 |
| Ubuntu 18.04 LTS | linux-oracle-5.4 | 5.4.0-1043.46~18.04.1 | USN-4917-1 |
| Ubuntu 18.04 LTS | linux-raspi-5.4 | 5.4.0-1034.37~18.04.1 | USN-4917-1 |
| Ubuntu 18.04 LTS | linux-raspi2 | 4.15.0-1084.89 | USN-4916-1 |
| Ubuntu 18.04 LTS | linux-raspi2-5.3 | 5.3.0-1039.41 | USN-4917-1 |
| Ubuntu 18.04 LTS | linux-snapdragon | 4.15.0-1101.110 | USN-4916-1 |
| Ubuntu 16.04 LTS | linux | 4.4.0-209.241 | USN-4916-1 |
| Ubuntu 16.04 LTS | linux-aws | 4.4.0-1127.141 | USN-4916-1 |
| Ubuntu 16.04 LTS | linux-aws-hwe | 4.15.0-1099.106~16.04.1 | USN-4916-1 |
| Ubuntu 16.04 LTS | linux-azure | 4.15.0-1113.126~16.04.1 | USN-4916-1 |
| Ubuntu 16.04 LTS | linux-gcp | 4.15.0-1098.111~16.04.1 | USN-4916-1 |
| Ubuntu 16.04 LTS | linux-hwe | 4.15.0-142.146~16.04.1 | USN-4916-1 |
| Ubuntu 16.04 LTS | linux-hwe-edge | No fix yet | — |
| Ubuntu 16.04 LTS | linux-kvm | 4.4.0-1092.101 | USN-4916-1 |
| Ubuntu 16.04 LTS | linux-oracle | 4.15.0-1070.78~16.04.1 | USN-4916-1 |
| Ubuntu 16.04 LTS | linux-raspi2 | 4.4.0-1151.162 | USN-4916-1 |
| Ubuntu 16.04 LTS | linux-snapdragon | 4.4.0-1155.165 | USN-4916-1 |
Show 10 more (older releases, extended support, other products)Fewer releases
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu Pro FIPS 20.04 LTS | linux-aws-fips +2 | No fix yet | — |
| Ubuntu Pro FIPS 18.04 LTS | linux-fips +3 | No fix yet | — |
| Ubuntu Pro FIPS 16.04 LTS | linux-fips | No fix yet | — |
| Ubuntu Pro FIPS-updates 20.04 LTS | linux-aws-fips | 5.4.0-1069.73+fips2 | — |
| Ubuntu Pro FIPS-updates 20.04 LTS | linux-azure-fips | 5.4.0-1073.76+fips1 | — |
| Ubuntu Pro FIPS-updates 20.04 LTS | linux-gcp-fips | 5.4.0-1067.71~20.04.1 | — |
| Ubuntu Pro FIPS-updates 18.04 LTS | linux-aws-fips | 4.15.0-2042.44 | — |
| Ubuntu Pro FIPS-updates 18.04 LTS | linux-azure-fips | 4.15.0-2025.28 | — |
| Ubuntu Pro FIPS-updates 18.04 LTS | linux-fips | 4.15.0-1058.66 | — |
| Ubuntu Pro FIPS-updates 16.04 LTS | linux-fips | 4.4.0-1061.67 | — |
| Ubuntu Pro 20.04 LTS | linux | 5.4.0-72.80 | LSN-0076-1 |
| Ubuntu Pro 20.04 LTS | linux-aws | 5.4.0-1045.47 | LSN-0076-1 |
| Ubuntu Pro 20.04 LTS | linux-azure | 5.4.0-1046.48 | LSN-0076-1 |
| Ubuntu Pro 20.04 LTS | linux-gcp | 5.4.0-1042.45 | LSN-0076-1 |
| Ubuntu Pro 20.04 LTS | linux-gke | 5.4.0-1042.44 | LSN-0076-1 |
| Ubuntu Pro 20.04 LTS | linux-gkeop | 5.4.0-1014.15 | LSN-0076-1 |
| Ubuntu Pro 18.04 LTS | linux | 4.15.0-142.146 | LSN-0076-1 |
| Ubuntu Pro 18.04 LTS | linux-aws | 4.15.0-1099.106 | LSN-0076-1 |
| Ubuntu Pro 18.04 LTS | linux-gke-5.4 | 5.4.0-1042.44~18.04.1 | LSN-0076-1 |
| Ubuntu Pro 18.04 LTS | linux-gkeop-5.4 | 5.4.0-1014.15~18.04.1 | LSN-0076-1 |
| Ubuntu Pro 18.04 LTS | linux-hwe-5.4 | 5.4.0-72.80~18.04.1 | LSN-0076-1 |
| Ubuntu Pro 18.04 LTS | linux-oem +1 | No fix yet | LSN-0076-1 |
| Ubuntu Pro 16.04 LTS | linux | 4.4.0-209.241 | LSN-0076-1 |
| Ubuntu Pro 16.04 LTS | linux-aws | 4.4.0-1127.141 | LSN-0076-1 |
| Ubuntu Pro 16.04 LTS | linux-azure | 4.15.0-1113.126~16.04.1 | LSN-0076-1 |
| Ubuntu Pro 16.04 LTS | linux-hwe | 4.15.0-142.146~16.04.1 | LSN-0076-1 |
| Ubuntu Pro 14.04 LTS | linux-aws | 4.4.0-1091.95 | USN-4916-1 |
| Ubuntu Pro 14.04 LTS | linux-azure | 4.15.0-1113.126~14.04.1 | USN-4916-1 |
| Ubuntu Pro 14.04 LTS | linux-lts-xenial | 4.4.0-209.241~14.04.1 | USN-4916-1, LSN-0076-1 |
Public exploits
Exploit or proof-of-concept code for this vulnerability is publicly available, which lowers the bar for attackers. Treat it as a reason to patch sooner.
Third-party code, not reviewed by us. Public PoCs are sometimes fake or contain malware. Read the code first and run it only in an isolated lab, against systems you are authorised to test.
Metasploit 1 module
-
2021 Ubuntu Overlayfs LPE
exploit/linux/local/cve_2021_3493_overlayfs
GitHub 21 repositories · most starred shown
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briskets/CVE-2021-3493 ★ 447 · Apr 19, 2021
Ubuntu OverlayFS Local Privesc
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inspiringz/CVE-2021-3493 ★ 42 · Jul 7, 2021
CVE-2021-3493 Ubuntu OverlayFS Local Privesc (Interactive Bash Shell & Execute Command Entered)
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oneoy/CVE-2021-3493 ★ 3 · Apr 22, 2021
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Ayham-Megdadi/Zero-Day-Legacy ★ 2 · Jul 5, 2026
A vulnerable Boot-to-Root CTF lab machine simulating a hospital environment. Features a realistic 17-step attack chain including SQL Injection, XSS, Session Hijacking, SSH access, password cracking, …
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puckiestyle/CVE-2021-3493 ★ 2 · Oct 2, 2021
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cerodah/overlayFS-CVE-2021-3493 ★ 2 · Sep 12, 2021
2021 kernel vulnerability in Ubuntu.
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fei9747/CVE-2021-3493 ★ 1 · Nov 29, 2022
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pmihsan/OverlayFS-CVE-2021-3493 ★ 0 · Jan 16, 2023
Exploit For OverlayFS
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derek-turing/CVE-2021-3493 ★ 0 · Jul 16, 2021
CVE-2021-3493 Ubuntu漏洞
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Abdennour-py/CVE-2021-3493 ★ 0 · May 2, 2021
Sources: PoC-in-GitHub, Metasploit Framework, Exploit-DB — updated daily. Only links are listed; no exploit code is hosted here.
Advisories 4
- USN-4916-1 linux, linux-aws, linux-aws-hwe, linux-azure, linux-azure-4.15, linux-dell300x, linux-gcp, linux-gcp-4.15, linux-hwe, linux-kvm, linux-lts-xenial, linux-oracle, linux-raspi2, linux-snapdragon vulnerabilities Ubuntu Security Notices (USN) · Jun 3, 2026
- USN-4917-1 linux, linux-aws, linux-aws-5.4, linux-azure, linux-azure-5.4, linux-gcp, linux-gcp-5.4, linux-gke-5.3, linux-gke-5.4, linux-gkeop, linux-gkeop-5.4, linux-hwe, linux-hwe-5.4, linux-hwe-5.8, linux-kvm, linux-oem-5.10, linux-oracle, linux-oracle-5.4, linux-raspi, linux-raspi-5.4, linux-raspi2-5.3 vulnerabilities Ubuntu Security Notices (USN) · Jun 3, 2026
- USN-4915-1 linux-oem-5.6 vulnerabilities Ubuntu Security Notices (USN) · Jun 3, 2026
- LSN-0076-1 Kernel Live Patch Security Notice Ubuntu Security Notices (USN) · Jun 3, 2026
References
- https://ubuntu.com/security/notices/USN-4917-1
- https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=7c03e2cda4a584cadc398e8f6641ca9988a39d52
- https://www.openwall.com/lists/oss-security/2021/04/16/1
- http://packetstormsecurity.com/files/162434/Kernel-Live-Patch-Security-Notice-LSN-0076-1.html
- http://packetstormsecurity.com/files/162866/Ubuntu-OverlayFS-Local-Privilege-Escalation.html
- http://packetstormsecurity.com/files/165151/Ubuntu-Overlayfs-Local-Privilege-Escalation.html