UBUNTU-CVE-2026-31402
In the Linux kernel, the following vulnerability has been resolved: nfsd: fix heap overflow in NFSv4.0 LOCK replay cache The NFSv4.0 replay cache uses a fixed 112-byte inline buffer (rp_ibuf[NFSD4_REPLAY_ISIZE]) to store encoded operation responses. This size was calculated based on OPEN responses and does not account for LOCK denied responses, which include the conflicting lock owner as a variable-length field up to 1024 bytes (NFS4_OPAQUE_LIMIT). When a LOCK operation is denied due to a conflict with an existing lock that has a large owner, nfsd4_encode_operation() copies the full encoded response into the undersized replay buffer via read_bytes_from_xdr_buf() with no bounds check. This results in a slab-out-of-bounds write of up to 944 bytes past the end of the buffer, corrupting adjacent heap memory. This can be triggered remotely by an unauthenticated attacker with two cooperating NFSv4.0 clients: one sets a lock with a large owner string, then the other requests a conflicting lock to provoke the denial. We could fix this by increasing NFSD4_REPLAY_ISIZE to allow for a full opaque, but that would increase the size of every stateowner, when most lockowners are not that large. Instead, fix this by checking the encoded response length against NFSD4_REPLAY_ISIZE before copying into the replay buffer. If the response is too large, set rp_buflen to 0 to skip caching the replay payload. The status is still cached, and the client already received the correct response on the original request.
02 / AFFECTED SOFTWARE
Affected packages
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35 explicit affected versions
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16 explicit affected versions
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26 explicit affected versions
45 explicit affected versions
37 explicit affected versions
49 explicit affected versions
14 explicit affected versions
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164 explicit affected versions
9 explicit affected versions
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11 explicit affected versions
38 explicit affected versions
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13 explicit affected versions
89 explicit affected versions
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6 explicit affected versions
7 explicit affected versions
96 explicit affected versions
120 explicit affected versions
4 explicit affected versions
8 explicit affected versions
1 explicit affected versions
1 explicit affected versions
1 explicit affected versions
87 explicit affected versions
77 explicit affected versions
77 explicit affected versions
13 explicit affected versions
43 explicit affected versions
76 explicit affected versions
13 explicit affected versions
119 explicit affected versions
10 explicit affected versions
8 explicit affected versions
44 explicit affected versions
87 explicit affected versions
14 explicit affected versions
4 explicit affected versions
76 explicit affected versions
78 explicit affected versions
13 explicit affected versions
11 explicit affected versions
1 explicit affected versions
67 explicit affected versions
122 explicit affected versions
18 explicit affected versions
38 explicit affected versions
03 / CONNECTIONS
Connected vulnerabilities
04 / EVIDENCE
Source records
In the Linux kernel, the following vulnerability has been resolved: nfsd: fix heap overflow in NFSv4.0 LOCK replay cache The NFSv4.0 replay cache uses a fixed 112-byte inline buffer (rp_ibuf[NFSD4_REPLAY_ISIZE]) to store encoded operation responses. This size was calculated based on OPEN responses and does not account for LOCK denied responses, which include the conflicting lock owner as a variable-length field up to 1024 bytes (NFS4_OPAQUE_LIMIT). When a LOCK operation is denied due to a conflict with an existing lock that has a large owner, nfsd4_encode_operation() copies the full encoded response into the undersized replay buffer via read_bytes_from_xdr_buf() with no bounds check. This results in a slab-out-of-bounds write of up to 944 bytes past the end of the buffer, corrupting adjacent heap memory. This can be triggered remotely by an unauthenticated attacker with two cooperating NFSv4.0 clients: one sets a lock with a large owner string, then the other requests a conflicting lock to provoke the denial. We could fix this by increasing NFSD4_REPLAY_ISIZE to allow for a full opaque, but that would increase the size of every stateowner, when most lockowners are not that large. Instead, fix this by checking the encoded response length against NFSD4_REPLAY_ISIZE before copying into the replay buffer. If the response is too large, set rp_buflen to 0 to skip caching the replay payload. The status is still cached, and the client already received the correct response on the original request.
05 / REFERENCES
Further evidence
- https://git.kernel.org/linus/5133b61aaf437e5f25b1b396b14242a6bb0508e2
- https://git.kernel.org/stable/c/0f0e2a54a31a7f9ad2915db99156114872317388
- https://git.kernel.org/stable/c/5133b61aaf437e5f25b1b396b14242a6bb0508e2
- https://git.kernel.org/stable/c/8afb437ea1f70cacb4bbdf11771fb5c4d720b965
- https://git.kernel.org/stable/c/ae8498337dfdfda71bdd0b807c9a23a126011d76
- https://git.kernel.org/stable/c/c9452c0797c95cf2378170df96cf4f4b3bca7eff
- https://git.kernel.org/stable/c/dad0c3c0a8e5d1d6eb0fc455694ce3e25e6c57d0
- https://ubuntu.com/security/CVE-2026-31402
- https://ubuntu.com/security/notices/USN-8490-1
- https://ubuntu.com/security/notices/USN-8490-2
- https://ubuntu.com/security/notices/USN-8491-1
- https://ubuntu.com/security/notices/USN-8492-1
- https://ubuntu.com/security/notices/USN-8492-2
- https://ubuntu.com/security/notices/USN-8492-3
- https://ubuntu.com/security/notices/USN-8492-4
- https://ubuntu.com/security/notices/USN-8492-5
- https://ubuntu.com/security/notices/USN-8493-1
- https://ubuntu.com/security/notices/USN-8493-2
- https://ubuntu.com/security/notices/USN-8497-1
- https://ubuntu.com/security/notices/USN-8498-1
- https://ubuntu.com/security/notices/USN-8499-1
- https://ubuntu.com/security/notices/USN-8501-1
- https://ubuntu.com/security/notices/USN-8508-1
- https://ubuntu.com/security/notices/USN-8527-1
- https://ubuntu.com/security/notices/USN-8528-1
- https://ubuntu.com/security/notices/USN-8529-1
- https://ubuntu.com/security/notices/USN-8529-2
- https://ubuntu.com/security/notices/USN-8530-1
- https://ubuntu.com/security/notices/USN-8530-2
- https://ubuntu.com/security/notices/USN-8545-1
- https://ubuntu.com/security/notices/USN-8546-1
- https://ubuntu.com/security/notices/USN-8547-1
- https://ubuntu.com/security/notices/USN-8547-2
- https://ubuntu.com/security/notices/USN-8548-1
- https://ubuntu.com/security/notices/USN-8548-2
- https://ubuntu.com/security/notices/USN-8604-1
- https://ubuntu.com/security/notices/USN-8605-1
- https://ubuntu.com/security/notices/USN-8606-1
- https://ubuntu.com/security/notices/USN-8607-1
- https://ubuntu.com/security/notices/USN-8609-1
- https://ubuntu.com/security/notices/USN-8615-1
- https://ubuntu.com/security/notices/USN-8615-2
- https://ubuntu.com/security/notices/USN-8616-1
- https://ubuntu.com/security/notices/USN-8619-1
- https://ubuntu.com/security/notices/USN-8635-1
- https://www.cve.org/CVERecord?id=CVE-2026-31402