CVE-2026-99077ipv4: udp: Create exceptions before socket matching
- 7.4HighCVSS base score
- 0.43%Exploitation in 30 daysEPSS · top 62% of all CVEs
- NoKnown exploitednot in CISA's KEV catalog
- NonePublic exploitsnone known yet
Description
In the Linux kernel, the following vulnerability has been resolved: ipv4: udp: Create exceptions before socket matching Currently, when ICMP Fragmentation Needed and Redirect Message packets are locally delivered and quote a UDP packet, a FIB nexthop exception (FNHE) is only created if the kernel can match the UDP packet to an existing socket. This behavior allows off-path attackers to conduct a side-channel attack on the FNHE cache in order to discover the ephemeral port used by a connected UDP socket. Commit 6457378fe796 ("ipv4: use siphash instead of Jenkins in fnhe_hashfun()") and commit 67d6d681e15b ("ipv4: make exception cache less predictible") tried to mitigate such attacks by making it harder for attackers to discover hash collisions in the FNHE cache and by randomizing the number of exceptions a hash bucket can hold, respectively. Unfortunately, both of the mitigations can be bypassed. Instead, mitigate such attacks by always creating a FNHE, even before trying to find a matching socket. Do that by calling ipv4_update_pmtu() and ipv4_redirect(), the helpers used when the quoted packet did not originate from a socket. This means that guesses (right or wrong) from an off-path attacker will always result in a FNHE being created or updated in the cache that the attacker can observe. Pass an oif of 0, in a similar fashion to icmp_err(). This is also the oif used by the socket path for sockets that are not bound to a device. Note that this does not allow attackers to create FNHEs that they could not create before, as both helpers can already be reached with little to no validation. For example, by sending an ICMP error that quotes an ICMP Echo Reply or one that quotes a UDP source port that matches a wildcard socket. Also note that in the good case (matched socket) the above scheme comes at the cost of an extra route lookup, as the no socket helpers perform their own lookup before the one performed by ipv4_sk_update_pmtu() / ipv4_sk_redirect(). When the two resolve to different nexthops, it also results in two exceptions being created for the same destination IP. One in the FNHE cache of the nexthop resolved by the no socket helpers and another in the FNHE cache of the nexthop used by the socket.
Timeline
ID reserved
By Linux
- 28 days later
· 28 days later
Published
- 7 days later
· 7 days later
Record updated
Changes after publication (a new score, a public exploit, EPSS crossing 1, 10 or 50 %, leaving KEV) are kept since November 2026; earlier ones are not known.
Scores
| Scored by | CVSS | Score | Vector |
|---|---|---|---|
| LinuxCNA (assigner) | 3.1 | High7.4 | CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N |
| NVDNVD · Received | 3.1 | High7.4 | CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N |
- EPSS (exploitation in 30 days)
- 0.43% · top 62% of all CVEs (13 Nov 2026)
The list uses the assigner's score when there is one, then CISA's, then NVD's: High 7.4.
Affected products
- affected 4895c771c7f006b4b90f9d6b1d2210939ba57b38 – < e8f211a37396f1684af9ac81b3fc53538eb9c2f7
- affected 4895c771c7f006b4b90f9d6b1d2210939ba57b38 – < 9f97b01ee799bdf57d9183623f3987c8bbfd4f6f
- affected 4895c771c7f006b4b90f9d6b1d2210939ba57b38 – < e0cd4942831d4ef8f6d4b90b0d3510460fdfbceb
- affected 4895c771c7f006b4b90f9d6b1d2210939ba57b38 – < 0cf0ff2f728f2a1434c56c0bcf267fe230abf124
- affected 4895c771c7f006b4b90f9d6b1d2210939ba57b38 – < 3b92e4349c6b0dd1e05d5f0483e71ef37691b1c3
- affected 4895c771c7f006b4b90f9d6b1d2210939ba57b38 – < ecd7ead4bf05e221e90f18a29aec570a50fd1592
- affected 4895c771c7f006b4b90f9d6b1d2210939ba57b38 – < be4fd05398f2b5e42029be70ee875fc749b8ce3a
- affected 4895c771c7f006b4b90f9d6b1d2210939ba57b38 – < 4c3499f79f8c7e8561266bcc220a18538cec0458
- affected 3.6
- unaffected < 3.6
- unaffected 5.10.273 – ≤ 5.10.*
- unaffected 5.15.224 – ≤ 5.15.*
- unaffected 6.1.191 – ≤ 6.1.*
- unaffected 6.6.161 – ≤ 6.6.*
- unaffected 6.12.115 – ≤ 6.12.*
- unaffected 6.18.59 – ≤ 6.18.*
- unaffected 7.2.11 – ≤ 7.2.*
- unaffected 7.3 – ≤ *
References
References8
- https://git.kernel.org/stable/c/e8f211a37396f1684af9ac81b3fc53538eb9c2f7 (opens in a new tab)
- https://git.kernel.org/stable/c/9f97b01ee799bdf57d9183623f3987c8bbfd4f6f (opens in a new tab)
- https://git.kernel.org/stable/c/e0cd4942831d4ef8f6d4b90b0d3510460fdfbceb (opens in a new tab)
- https://git.kernel.org/stable/c/0cf0ff2f728f2a1434c56c0bcf267fe230abf124 (opens in a new tab)
- https://git.kernel.org/stable/c/3b92e4349c6b0dd1e05d5f0483e71ef37691b1c3 (opens in a new tab)
- https://git.kernel.org/stable/c/ecd7ead4bf05e221e90f18a29aec570a50fd1592 (opens in a new tab)
- https://git.kernel.org/stable/c/be4fd05398f2b5e42029be70ee875fc749b8ce3a (opens in a new tab)
- https://git.kernel.org/stable/c/4c3499f79f8c7e8561266bcc220a18538cec0458 (opens in a new tab)
Sources
The same CVE in the primary databases and aggregators, to check against.
- CVE.org record (opens in a new tab)
- CVE List JSON (GitHub) (opens in a new tab)
- NVD (opens in a new tab)
- FIRST EPSS (opens in a new tab)
- EUVD EUVD-2026-108743 (opens in a new tab)
- OSV.dev (opens in a new tab)
- GitHub Advisories (opens in a new tab)
- CIRCL Vulnerability-Lookup (opens in a new tab)
Badge for a README or a ticket
[](https://cveledger.app/cve/CVE-2026-99077)Record last updated .