Description
Shiftfs, an out-of-tree stacking file system included in Ubuntu Linux kernels, did not properly handle faults occurring during copy_from_user() correctly. These could lead to either a double-free situation or memory not being freed at all. An attacker could use this to cause a denial of service (kernel memory exhaustion) or gain privileges via executing arbitrary code. AKA ZDI-CAN-13562.
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 | 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.
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-raspi2 | No fix yet | — |
| Ubuntu 20.04 LTS | linux-riscv-5.8 | 5.8.0-22.24~20.04.1 | — |
| 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-5.4 | 5.4.0-1046.48~18.04.1 | USN-4917-1 |
| Ubuntu 18.04 LTS | linux-gcp +10 | No fix yet | — |
| 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-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-raspi2-5.3 | 5.3.0-1039.41 | USN-4917-1 |
| Ubuntu 16.04 LTS | linux-hwe-edge | No fix yet | — |
Show 4 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-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 20.04 LTS | linux | 5.4.0-72.80 | LSN-0077-1 |
| Ubuntu Pro 20.04 LTS | linux-gcp | 5.4.0-1042.45 | LSN-0077-1 |
| Ubuntu Pro 20.04 LTS | linux-gke | 5.4.0-1042.44 | LSN-0077-1 |
| Ubuntu Pro 20.04 LTS | linux-gkeop | 5.4.0-1014.15 | LSN-0077-1 |
| Ubuntu Pro 18.04 LTS | linux-gke-5.4 | 5.4.0-1042.44~18.04.1 | LSN-0077-1 |
| Ubuntu Pro 18.04 LTS | linux-gkeop-5.4 | 5.4.0-1014.15~18.04.1 | LSN-0077-1 |
| Ubuntu Pro 18.04 LTS | linux-hwe-5.4 | 5.4.0-72.80~18.04.1 | LSN-0077-1 |
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.
GitHub 1 repository
-
synacktiv/CVE-2021-3492 ★ 42 · Jun 28, 2021
PoC for CVE-2021-3492 used at Pwn2Own 2021
Sources: PoC-in-GitHub, Metasploit Framework, Exploit-DB — updated daily. Only links are listed; no exploit code is hosted here.
Advisories 3
- 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-0077-1 Kernel Live Patch Security Notice Ubuntu Security Notices (USN) · Jun 3, 2026
References
- https://www.openwall.com/lists/oss-security/2021/04/16/2
- https://git.launchpad.net/~ubuntu-kernel/ubuntu/+source/linux/+git/focal/commit/?id=8fee52ab9da87d82bc6de9ebb3480fff9b4d53e6
- https://git.launchpad.net/~ubuntu-kernel/ubuntu/+source/linux/+git/focal/commit/?id=25c891a949bf918b59cbc6e4932015ba4c35c333
- https://ubuntu.com/security/notices/USN-4917-1
- https://www.zerodayinitiative.com/advisories/ZDI-21-422/
- http://packetstormsecurity.com/files/162614/Kernel-Live-Patch-Security-Notice-LSN-0077-1.html