SB2026102388 - Observable discrepancy in Linux kernel ipv4

Description

This security bulletin contains information about 1 vulnerability.

1) Observable discrepancy (CVE-ID: CVE-2026-99077)

CWE-ID: CWE-203 - Observable discrepancy

CVSSv4: 6.3 [CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N]

The vulnerability allows a remote attacker to discover the ephemeral port used by a connected UDP socket through a cache side channel.

The vulnerability exists due to an observable discrepancy in IPv4 UDP error handling in the Linux kernel when processing locally delivered ICMP Fragmentation Needed or Redirect messages that quote UDP packets. A remote attacker can send crafted ICMP messages containing guessed UDP ports and observe changes in the FIB nexthop exception (FNHE) cache to distinguish packets matching an existing socket and discover its ephemeral port.

Remediation

Install update from vendor's website.

References

• https://git.kernel.org/stable/c/4c3499f79f8c7e8561266bcc220a18538cec0458
• https://git.kernel.org/stable/c/be4fd05398f2b5e42029be70ee875fc749b8ce3a