CVE-2026-99040: Linux Vulnerability

Description

In the Linux kernel, the following vulnerability has been resolved: KEYS: Fix add_key() race with keyring restriction __key_create_or_update() snapshots keyring->restrict_link before taking the destination keyring's semaphore. keyring_restrict() installs a restriction while holding that semaphore. This allows a writer to observe no restriction, wait for the keyring owner to install a reject-all restriction and return successfully, and then link a key using the stale NULL snapshot. The writer only needs write permission on the destination keyring. Move the restrict_link read after __key_link_lock() and __key_link_begin(). The read and the subsequent restriction check are then serialized with restriction installation by keyring->sem. The race was reproduced on v7.2.8 in 19 executions where restriction installation returned before the link completed. All 19 linked the key despite the reject-all restriction. With this change, 312 executions reached the same ordering and every add_key() call failed with -EPERM. The issue was found by manual concurrency analysis assisted by AI-based analysis and independently verified with a QEMU reproducer and kernel instrumentation.

Metrics

EPSS Probability

0.18%

7.7th percentile

Probability of exploitation in the next 30 days. Learn more

Affected Software

Source: CNA advisory (CVE.org). NVD analysis pending.

Vendor	Product	Versions
Linux	Linux	>= 5ac7eace2d00eab5ae0e9fdee63e38aee6001f7c, < 24806fc9bca28fa1433bf938d1424dcb45d80e50; >= 5ac7eace2d00eab5ae0e9fdee63e38aee6001f7c, < 9a5c2700336878465a630804a2d21864f22eca9c; >= 5ac7eace2d00eab5ae0e9fdee63e38aee6001f7c, < b3e404550dc2b7f3d4bb64b1da8005a1fa9a798d; >= 5ac7eace2d00eab5ae0e9fdee63e38aee6001f7c, < 305f1828b871dd46bf41addeb6f11d2c162dcb25; >= 5ac7eace2d00eab5ae0e9fdee63e38aee6001f7c, < f99399b48e3edd6851fac34cd329bab9f1f33baf; >= 5ac7eace2d00eab5ae0e9fdee63e38aee6001f7c, < 11516a0c402a6c1fa52254aa70d8d65fb921e59e; >= 5ac7eace2d00eab5ae0e9fdee63e38aee6001f7c, < da0b595d8e6e2dd798f6e34e09dc51a13b888514; >= 5ac7eace2d00eab5ae0e9fdee63e38aee6001f7c, < dd3ea3fcba7c75493760cdbccd35f029597e8d5e
Linux	Linux	4.7

References

Timeline

Published: Oct 23, 2026
Last Modified: Oct 30, 2026
Status: Received

Frequently Asked Questions

What is CVE-2026-99040?

In the Linux kernel, the following vulnerability has been resolved: KEYS: Fix add_key() race with keyring restriction __key_create_or_update() snapshots keyring->restrict_link before taking the destination keyring's semaphore. keyring_restrict() installs a restriction while holding that semaphore. This allows a writer to observe no restriction, wait for the keyring owner to install a reject-all restriction and return successfully, and then link a key using the stale NULL snapshot. The writer only needs write permission on the destination keyring. Move the restrict_link read after __key_link_lock() and __key_link_begin(). The read and the subsequent restriction check are then serialized with restriction installation by keyring->sem. The race was reproduced on v7.2.8 in 19 executions where restriction installation returned before the link completed. All 19 linked the key despite the reject-all restriction. With this change, 312 executions reached the same ordering and every add_key() call failed with -EPERM. The issue was found by manual concurrency analysis assisted by AI-based analysis and independently verified with a QEMU reproducer and kernel instrumentation.

How severe is CVE-2026-99040?

Severity scoring for CVE-2026-99040 is pending analysis. The EPSS model estimates a 0.18% probability of exploitation in the next 30 days.

How do I fix CVE-2026-99040?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

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