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CVE-2025-21972: net: mctp: unshare packets when reassembling

• Severity: medium (CVSS 5.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.3% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2025-04-01 · updated 2026-10-30
• Weakness: CWE-401

Description

In the Linux kernel, the following vulnerability has been resolved: net: mctp: unshare packets when reassembling Ensure that the frag_list used for reassembly isn't shared with other packets. This avoids incorrect reassembly when packets are cloned, and prevents a memory leak due to circular references between fragments and their skb_shared_info. The upcoming MCTP-over-USB driver uses skb_clone which can trigger the problem - other MCTP drivers don't share SKBs. A kunit test is added to reproduce the issue.

Affected products

• Linux kernel: from 5.15 before 6.12.20; from 6.13 before 6.13.8; 6.14-rc1, 6.14-rc2, 6.14-rc3, 6.14-rc4, 6.14-rc5, 6.14-rc6 — fixed in 6.12.20, 6.13.8
• Linux: 5.15 — fixed in 6.14

How to fix

Upgrade to a fixed version: Linux kernel 6.12.20, 6.13.8; Linux 6.14. Check the vendor advisory for mitigations.

References

• https://git.kernel.org/stable/c/3d0281d0713952e8dd14d6d47e3a9c345c28a3b7
• https://git.kernel.org/stable/c/5c47d5bfa7b096cf8890afac32141c578583f8e0
• https://git.kernel.org/stable/c/771087069a27c35c0a9fd7cc74fe7725b189b96b
• https://git.kernel.org/stable/c/f44fff3d3c6cd67b6f348b821d73c4d6888c7a6e
• https://git.kernel.org/stable/c/f5d83cf0eeb90fade4d5c4d17d24b8bee9ceeecc

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