What’s Vulnerable › Vulnerabilities

CVE-2021-33624

• Severity: medium (CVSS 4.7 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.9% probability of exploitation in the next 30 days
• Public exploit or detection template: yes
• Published: 2021-06-23 · updated 2026-10-08
• Weakness: CWE-843

Description

In kernel/bpf/verifier.c in the Linux kernel before 5.12.13, a branch can be mispredicted (e.g., because of type confusion) and consequently an unprivileged BPF program can read arbitrary memory locations via a side-channel attack, aka CID-9183671af6db.

Affected products

• Debian Linux: 9.0
• Linux kernel: before 5.12.13 — fixed in 5.12.13

How to fix

Upgrade to a fixed version: Linux kernel 5.12.13. Check the vendor advisory for mitigations.

References

• http://www.openwall.com/lists/oss-security/2021/06/21/1
• https://github.com/benschlueter/CVE-2021-33624
• https://github.com/torvalds/linux/commit/9183671af6dbf60a1219371d4ed73e23f43b49db
• https://lists.debian.org/debian-lts-announce/2021/10/msg00010.html
• https://www.usenix.org/conference/usenixsecurity21/presentation/kirzner
• http://www.openwall.com/lists/oss-security/2021/06/21/1
• https://github.com/torvalds/linux/commit/9183671af6dbf60a1219371d4ed73e23f43b49db
• https://lists.debian.org/debian-lts-announce/2021/10/msg00010.html
• https://www.usenix.org/conference/usenixsecurity21/presentation/kirzner

Get alerted when CVE-2021-33624 or the next vulnerability affects your stack