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Linux KernelOperating system · Linux

CVE-2026-31503

MEDIUM · 5.5 CVSS v3.1 Published 2026-04-22
Fix available
A fix is available. Upgrade to 6.1.168 / 6.6.131 or later.
See remediation →
57/100
Remediation priority · Elevated
Zero-click Patch available

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
In 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.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis

A detailed technical summary for this CVE is being prepared.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
Linux KernelOperating system
Affected:>= 2.6.33.1, < 6.1.168>= 6.2, < 6.6.131>= 6.7, < 6.12.80>= 6.13, < 6.18.21>= 6.19, < 6.19.11= 2.6.33= 7.0

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Local
Complexity
Low
Privileges
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

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 6.1.168 / 6.6.131 / 6.12.80 or later
Fixed in 6.1.1686.6.1316.12.80
Vendor patch git.kernel.org →
Recommended fix High confidence

Upgrade to kernel 6.1.168+, 6.6.131+, 6.12.80+, or 6.18.21+ depending on current branch

  1. 1. Identify current kernel version using `uname -r`
  2. 2. Determine which version branch your kernel is on (e.g., 6.1.x, 6.6.x, 6.12.x, 6.13.x)
  3. 3. For kernels >= 2.6.33.1 and < 6.1.168: upgrade to kernel version 6.1.168 or later in the 6.1 branch
  4. 4. For kernels >= 6.2 and < 6.6.131: upgrade to kernel version 6.6.131 or later in the 6.6 branch
  5. 5. For kernels >= 6.7 and < 6.12.80: upgrade to kernel version 6.12.80 or later in the 6.12 branch
  6. 6. For kernels >= 6.13 and < 6.18.21: upgrade to kernel version 6.18.21 or later in the 6.18 branch
  7. 7. After upgrading, reboot the system to load the fixed kernel
  8. 8. Verify the fix is applied by checking the kernel version and reviewing the commit (0a360f7f73a06ac88f18917055fbcc79694252d7) is included
Caveat Kernel upgrades may require driver rebuilds or system reboots; ensure compatibility with hardware and installed modules before upgrading

Generated from the published advisory — verify against the referenced sources before acting.

We can perform the upgrade in your staging environment and verify nothing breaks — typical engagement from $1,600. Get the upgrade done

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

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