CVE-2026-31503

Home/CVE/In the Linux kernel, the following vulnerability has been resolved: udp: Fix wildcard bind conflict check when using ha

CVE

In the Linux kernel, the following vulnerability has been resolved: udp: Fix wildcard bind conflict check when using ha

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.

MEDIUM · CVSS 5.5 EPSS 0.00015

Monitor

No active-exploitation, high-EPSS, or public-exploit signals - routine patching cadence

Sigma rules0 YARA rules0

Look this up elsewhere - one-click external pivots

NVD CVE.org CISA Vulners Exploit-DB GitHub PoC VulnCheck KEV GreyNoise

▸ How to read a CVE - triage first, then detect and patch

This page is every public fact about CVE-2026-31503, cross-linked. Its job is to answer one question fast - does this need my attention now? - and then hand you the two things you do about it. Here is how an analyst reads it.

Triage: should I act now? Four signals, and they are not interchangeable:

CVSSseverity - how bad it is IF exploited, 0-10. A high CVSS alone is not urgency; a flaw can be a perfect 10 and never actually be attacked. EPSSprobability - a model’s estimate of the chance it is exploited in the next 30 days, 0-1. This is the “will it actually happen” signal. CISA KEVconfirmed - it is being exploited in the wild right now. The strongest signal on the page; KEV beats any score. Weaponisedavailability - public exploits / PoCs, and especially Metasploit modules rated Excellent / Great. Reliable, packaged exploit code means low-skill attackers can use it today.

How they combine: KEV, or a dependable Metasploit module, means patch now regardless of CVSS. High CVSS + low EPSS + no exploit is real but not an emergency - schedule it. Low CVSS but KEV-listed still gets patched now. The verdict above already weighed these for you; this is how it got there.

Then what - two workflows:

Detectwhen you cannot patch today, follow this CVE to the ATT&CK techniques it enables, then Build a SIEM detection (the green button) - author a rule, test it in Atomic, deploy it. That buys visibility while the patch waits. PatchAffected products / packages tell you if you are exposed; Fixed versions by distribution and Vendor advisories give the exact version that closes it.

Reading order for the panels below: verdict + badges, then Public exploits / Metasploit (is it weaponised), then ATT&CK techniques + Sigma / IDS rules (can I detect it), then Affected products / packages + Fixed versions (am I exposed, what patches it), then Threat actors / IOCs (who uses it), then Scoring & timeline / references (the evidence).

View attack path from CVE-2026-31503

◆

ATT&CK techniques

Techniques this CVE enables - linked via CWECAPECATT&CK. High◆ = named directly in ATT&CK or Nuclei templates.

T1068 · Exploitation for Privilege Escalation

▤ Build a SIEM detection for these techniques

▤

Affected Products & Versions

linux kernel>= 2.6.33.1 and < 6.1.168
linux kernel>= 6.2 and < 6.6.131
linux kernel>= 6.7 and < 6.12.80
linux kernel>= 6.13 and < 6.18.21
linux kernel>= 6.19 and < 6.19.11
linux kernelall versions

▣

Scoring & Timeline

5.5

MEDIUM · CVSS v3.1 · 416baaa9-dc9f-4396-8d5f-8c081fb06d67

View on NVD

Attack Vector

Network Adjacent Local Physical

Attack Complexity

Low High

Privileges Required

None Low High

User Interaction

None Required

Scope

Unchanged Changed

Confidentiality

None Low High

Integrity

None Low High

Availability

None Low High

Published to NVD22 Apr 2026 · 02:16 PM

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

⚑

Vendor Advisories

suse-csafopenSUSE-SU-2026:20826-1
suse-csafSUSE-SU-2026:21841-1
suse-csafSUSE-SU-2026:21845-1
suse-csafSUSE-SU-2026:21860-1
msrcCVE-2026-31503

🔗

References & Sources

Source URLs (vendor pages, mailing lists, write-ups). Exploit/PoC links are in their own section above to avoid duplication.

https://git.kernel.org/stable/c/0a360f7f73a06ac88f18917055fbcc79694252d7Patch

https://git.kernel.org/stable/c/18d84c45def3671d5c89fbdd5d4ab8a3217fe4b4Patch

https://git.kernel.org/stable/c/2297e38114316b26ae02f2d205c49b5511c5ed55Patch

https://git.kernel.org/stable/c/d6ace0dbcbb7fd285738bb87b42b71b01858c952Patch

https://git.kernel.org/stable/c/e537dd15d0d4ad989d56a1021290f0c674dd8b28Patch

https://git.kernel.org/stable/c/f1bed05a832ae79be5f7a105da56810eaa59a5f1Patch