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CVE-2026-45884: apparmor: avoid per-cpu hold underflow in aa_get_buffer

• Severity: medium (CVSS 5.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.2% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-05-27 · updated 2026-06-25
• Weakness: CWE-191

Description

In the Linux kernel, the following vulnerability has been resolved: apparmor: avoid per-cpu hold underflow in aa_get_buffer When aa_get_buffer() pulls from the per-cpu list it unconditionally decrements cache->hold. If hold reaches 0 while count is still non-zero, the unsigned decrement wraps to UINT_MAX. This keeps hold non-zero for a very long time, so aa_put_buffer() never returns buffers to the global list, which can starve other CPUs and force repeated kmalloc(aa_g_path_max) allocations. Guard the decrement so hold never underflows.

Affected products

• Linux kernel: from 6.7 before 6.12.75; from 6.13 before 6.18.14; from 6.19 before 6.19.4 — fixed in 6.12.75, 6.18.14, 6.19.4

How to fix

Upgrade to a fixed version: Linux kernel 6.12.75, 6.18.14, 6.19.4. Check the vendor advisory for mitigations.

References

• https://git.kernel.org/stable/c/202824a1f89a9786c20a3d646a7c88d223abb1b2
• https://git.kernel.org/stable/c/4bcddd0f6b2e52b4c7b520e4d36a115caf5b7169
• https://git.kernel.org/stable/c/640cf2f09575c9dc344b3f7be2498d31e3923ead
• https://git.kernel.org/stable/c/80c334acc6d0bee8605a358a33e69b4aea1ffb92

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