---
title: "CVE-2026-99077: Linux Kernel - Information Disclosure"
description: "Linux kernel contains a side-channel vulnerability in IPv4 UDP handling caused by conditional creation of FIB nexthop exceptions only after socket matching, letting off-path attackers discover ephemeral UDP ports, exploit requires sending crafted ICMP packets."
url: https://panop.io/threat-heartbeat/CVE-2026-99077/
---

# CVE-2026-99077 Linux Kernel - Information Disclosure

Linux kernel contains a side-channel vulnerability in IPv4 UDP handling caused by conditional creation of FIB nexthop exceptions only after socket matching, letting off-path attackers discover ephemeral UDP ports, exploit requires sending crafted ICMP packets.

CVSS base score 7.4 /10

High

CISA KEV

Not listed

Public exploit

None known

Authentication

Not required

EPSS

0.21% chance of exploitation in 30 days

[View the NVD record ↗](https://nvd.nist.gov/vuln/detail/CVE-2026-99077)

## Details

Type

Information Disclosure

Impact

Information Disclosure

CVSS vector

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

Published

23 October 2026

Updated

25 October 2026

## Vendor fix

Update to the latest Linux kernel version containing the fix for FNHE creation before socket matching.

Patching closes this CVE. It does not tell you which of your systems run the affected version, or what else is exposed alongside them.

## References

- [https://nvd.nist.gov/vuln/detail/CVE-2026-99077](https://nvd.nist.gov/vuln/detail/CVE-2026-99077)
- [https://git.kernel.org/stable/c/4c3499f79f8c7e8561266bcc220a18538cec0458](https://git.kernel.org/stable/c/4c3499f79f8c7e8561266bcc220a18538cec0458)
- [https://git.kernel.org/stable/c/be4fd05398f2b5e42029be70ee875fc749b8ce3a](https://git.kernel.org/stable/c/be4fd05398f2b5e42029be70ee875fc749b8ce3a)

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## What this record can't tell you

- Whether you run the affected software, and where
- Whether an attacker can actually reach and exploit it
- The misconfigurations that never get a CVE number
- What it would cost the business, ranked into what to fix first

Panop answers these inside your environment, for this CVE and every other finding.

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