Port disclosure via socket-dependent exception caching
Published Oct 23, 2026 · Updated Oct 23, 2026
Linux IPv6 UDP handling exposes ephemeral ports to remote attackers through a side channel triggered by crafted ICMPv6 errors. The udpv6_err path in net/ipv6/udp.c creates cache exceptions for Packet Too Big and Redirect messages quoting UDP packets only after matching an existing socket, making correct port guesses distinguishable. Exploitation requires a connected UDP socket and observable effects in its nexthop's exception cache; the disclosed impact is indirect port disclosure.
Summary
What happened
Linux IPv6 UDP handling exposes ephemeral ports to remote attackers through a side channel triggered by crafted ICMPv6 errors. The udpv6_err path in net/ipv6/udp.c creates cache exceptions for Packet Too Big and Redirect messages quoting UDP packets only after matching an existing socket, making correct port guesses distinguishable. Exploitation requires a connected UDP socket and observable effects in its nexthop's exception cache; the disclosed impact is indirect port disclosure.
The record
- CVE
- CVE-2026-99076
- Published
- Oct 23, 2026
- Updated
- Oct 23, 2026
- Vendor
- The Linux Kernel Organization
- Product
- Linux
- Classifications
- Unavailable
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Oct 23, 2026CVE publishedPublication date reported by the CVE source.
- Oct 23, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=2b760fcf5cfb34e8610df56d83745b2b74ae1379 <8c9b310c958be33ba8fb9d0e6b77811d013e10c0
- Affected versionversion=2b760fcf5cfb34e8610df56d83745b2b74ae1379 <ac76cab50e899a7346408b8d3c3a4192c2eefb9f
- Affected versionversion=4.15
What conditions does exploitation require?
What is affected?
Published CVSS scores
No CVSS assessment is available in this record.
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Activity data is delayed. The latest report is Sep 28, 2026.
Weakness, pattern, technique
No sourced classifications are available.
Public exploit references
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Technologies
Your stack
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Your stack
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