CVE-2026-99077: Linux kernel · ipv4: udp: Create exceptions before socket matching
Affects Linux kernelSource CVE Database V5
Not known to be exploited · CVSS 7.4 High : upgrade to be4fd05398f2b5e42029be70ee875fc749b8ce3a or 4c3499f79f8c7e8561266bcc220a18538cec0458 soon.
Data as of 26 Oct 2026, 13:07 UTC
- 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:NExploitation evidence
Disclosed: evidence found.
CVE published 23 Oct 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by 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
| Product | Affected | Fixed in |
|---|---|---|
| LinuxLinux | Affected
| Fixed in
|
| LinuxLinux | Affected
| Fixed in
|
| LinuxLinux | Affected
| 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.