udp: Fix wildcard bind conflict check when using hash2

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Summary

CVECVE-2026-31503
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-04-22 14:16:48 UTC
Updated2026-04-28 15:07:47 UTC
DescriptionIn the Linux kernel, the following vulnerability has been resolved: udp: Fix wildcard bind conflict check when using hash2 When binding a udp_sock to a local address and port, UDP uses two hashes (udptable->hash and udptable->hash2) for collision detection. The current code switches to "hash2" when hslot->count > 10. "hash2" is keyed by local address and local port. "hash" is keyed by local port only. The issue can be shown in the following bind sequence (pseudo code): bind(fd1, "[fd00::1]:8888") bind(fd2, "[fd00::2]:8888") bind(fd3, "[fd00::3]:8888") bind(fd4, "[fd00::4]:8888") bind(fd5, "[fd00::5]:8888") bind(fd6, "[fd00::6]:8888") bind(fd7, "[fd00::7]:8888") bind(fd8, "[fd00::8]:8888") bind(fd9, "[fd00::9]:8888") bind(fd10, "[fd00::10]:8888") /* Correctly return -EADDRINUSE because "hash" is used * instead of "hash2". udp_lib_lport_inuse() detects the * conflict. */ bind(fail_fd, "[::]:8888") /* After one more socket is bound to "[fd00::11]:8888", * hslot->count exceeds 10 and "hash2" is used instead. */ bind(fd11, "[fd00::11]:8888") bind(fail_fd, "[::]:8888") /* succeeds unexpectedly */ The same issue applies to the IPv4 wildcard address "0.0.0.0" and the IPv4-mapped wildcard address "::ffff:0.0.0.0". For example, if there are existing sockets bound to "192.168.1.[1-11]:8888", then binding "0.0.0.0:8888" or "[::ffff:0.0.0.0]:8888" can also miss the conflict when hslot->count > 10. TCP inet_csk_get_port() already has the correct check in inet_use_bhash2_on_bind(). Rename it to inet_use_hash2_on_bind() and move it to inet_hashtables.h so udp.c can reuse it in this fix.

Risk And Classification

Primary CVSS: v3.1 5.5 MEDIUM from [email protected]

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

EPSS: 0.000240000 probability, percentile 0.067930000 (date 2026-04-26)

Problem Types: NVD-CWE-noinfo

CVSS v3.1 Breakdown

Attack Vector
Local
Attack Complexity
Low
Privileges Required
Low
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

NVD Known Affected Configurations (CPE 2.3)

TypeVendorProductVersionUpdateEditionLanguage
Operating System Linux Linux Kernel All All All All

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected 30fff9231fad757c061285e347b33c5149c2c2e4 d6ace0dbcbb7fd285738bb87b42b71b01858c952 git Not specified
CNA Linux Linux affected 30fff9231fad757c061285e347b33c5149c2c2e4 2297e38114316b26ae02f2d205c49b5511c5ed55 git Not specified
CNA Linux Linux affected 30fff9231fad757c061285e347b33c5149c2c2e4 f1bed05a832ae79be5f7a105da56810eaa59a5f1 git Not specified
CNA Linux Linux affected 30fff9231fad757c061285e347b33c5149c2c2e4 18d84c45def3671d5c89fbdd5d4ab8a3217fe4b4 git Not specified
CNA Linux Linux affected 30fff9231fad757c061285e347b33c5149c2c2e4 0a360f7f73a06ac88f18917055fbcc79694252d7 git Not specified
CNA Linux Linux affected 30fff9231fad757c061285e347b33c5149c2c2e4 e537dd15d0d4ad989d56a1021290f0c674dd8b28 git Not specified
CNA Linux Linux affected 2.6.33 Not specified
CNA Linux Linux unaffected 2.6.33 semver Not specified
CNA Linux Linux unaffected 6.1.168 6.1.* semver Not specified
CNA Linux Linux unaffected 6.6.131 6.6.* semver Not specified
CNA Linux Linux unaffected 6.12.80 6.12.* semver Not specified
CNA Linux Linux unaffected 6.18.21 6.18.* semver Not specified
CNA Linux Linux unaffected 6.19.11 6.19.* semver Not specified
CNA Linux Linux unaffected 7.0 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/18d84c45def3671d5c89fbdd5d4ab8a3217fe4b4 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/2297e38114316b26ae02f2d205c49b5511c5ed55 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/d6ace0dbcbb7fd285738bb87b42b71b01858c952 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/0a360f7f73a06ac88f18917055fbcc79694252d7 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/e537dd15d0d4ad989d56a1021290f0c674dd8b28 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/f1bed05a832ae79be5f7a105da56810eaa59a5f1 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
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