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VulnerabilityPublished Updated

CVE-2026-99077: Linux kernel · ipv4: udp: Create exceptions before socket matching

Affects Linux kernelSource CVE Database V5

0

Not known to be exploited · CVSS 7.4 High : upgrade to be4fd05398f2b5e42029be70ee875fc749b8ce3a or 4c3499f79f8c7e8561266bcc220a18538cec0458 soon.

Data as of 26 Oct 2026, 13:07 UTC

CVSS 3.1 base score
7.4High
How severe the flaw is on the 0–10 CVSS scale.
EPSS
0.3% chance of exploitation in 30 days – higher than 24% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch
Available – fixed in be4fd05398f2b5e42029be70ee875fc749b8ce3a, 4c3499f79f8c7e8561266bcc220a18538cec0458
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 23 Oct 2026

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponised: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq Mirage: no evidence on record.

    No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.

What to do

Upgrade Linux kernel to be4fd05398f2b5e42029be70ee875fc749b8ce3a or 4c3499f79f8c7e8561266bcc220a18538cec0458.

Affected software

ProductAffectedFixed in
LinuxLinuxAffected
  • ≥ 4895c771c7f006b4b90f9d6b1d2210939ba57b38, < be4fd05398f2b5e42029be70ee875fc749b8ce3a
Fixed in
  • be4fd05398f2b5e42029be70ee875fc749b8ce3a
LinuxLinuxAffected
  • ≥ 4895c771c7f006b4b90f9d6b1d2210939ba57b38, < 4c3499f79f8c7e8561266bcc220a18538cec0458
Fixed in
  • 4c3499f79f8c7e8561266bcc220a18538cec0458
LinuxLinuxAffected
  • =3.6
Fixed in–

AI-suggested

A fix is available and included in Linux kernel commits be4fd05398f2b5e42029be70ee875fc749b8ce3a and 4c3499f79f8c7e8561266bcc220a18538cec0458. Users and administrators should update to these fixed kernel versions or later to remediate this vulnerability. No additional mitigation steps are indicated by the vendor advisory.

Description

CVE-2026-99077 is a vulnerability in the Linux kernel's IPv4 UDP implementation where exceptions in the FIB nexthop exception (FNHE) cache are only created after matching a UDP packet to an existing socket. This allows off-path attackers to perform side-channel attacks to discover ephemeral UDP ports. The vulnerability is mitigated by changing the behavior to always create FNHE entries before socket matching, preventing attackers from inferring socket information via cache side-channels.

References

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