CVE-2026-63920: ipv6: validate extension header length before copying to cmsg
Telemetry drift only. No threshold crossed and no authority ruling changed.
CVE record, CISA KEV and EPSS as of 2026-10-18.
CVEs like this one computed, by meaning
What to do now held facts and links
- Upgrade to the fixed version for your release line, or later: 5.10.259; 5.15.210; 6.1.176; 6.6.143; 6.12.93; 6.18.35; 7.0.12; 7.1 CVE record
- Record your decision, dated and frozen with today's evidence: patch by a date · mitigated by a compensating control · deferred · accepted the risk · not affected
- Check your version against the ranges this record publishes.
What it is stated by the CNA
In the Linux kernel, the following vulnerability has been resolved: ipv6: validate extension header length before copying to cmsg ip6_datagram_recv_specific_ctl() builds IPV6_{HOPOPTS,DSTOPTS,RTHDR} cmsgs (and their IPV6_2292* legacy counterparts) by trusting the on-wire hdrlen byte (ptr[1]) when computing the put_cmsg() length. The length was validated only at parse time (ipv6_parse_hopopts(), etc.). An nftables payload-write expression can rewrite hdrlen after parsing and before the skb reaches recvmsg; the write itself is in-bounds but put_cmsg() then reads up to ((hdrlen+1) << 3) = 2040 bytes from an 8-byte header. …
- weakness
- Not named by the CNA.
- affected
- Linux
- versions
- No affected-version range in held sources.
- fixed in
- 5.10.259; 5.15.210; 6.1.176; 6.6.143; 6.12.93; 6.18.35; 7.0.12; 7.1
- fixed by package (from OSV advisories)
- Kernel (Linux): 5.10.259; 5.15.210; 6.1.176; 6.18.35; 7.0.12; 6.6.143; 6.12.93 CVE-2026-63920
- severity
- 7.1 CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H
- assigned by
- Linux
- published
- 2026-07-19
check us git.kernel.org git.kernel.org git.kernel.org git.kernel.org
Exploit code held, dated
- exploit code
- None held in the PoC-in-GitHub feed. A public repository changes this brief.
What moved held, dated
| date | EPSS | event |
|---|---|---|
| 20 Jul 2026 | 0.0021 | |
| 21 Jul 2026 | 0.00159 | |
| 28 Aug 2026 | 0.00167 | |
| 28 Sep 2026 | 0.00171 |
4 observations held. A step marked with a scoring model moved because the measurement was replaced, not because the vulnerability changed.
Outside the record researched, cited
This section reads the record's references and adds cited findings from outside it. It needs an account. Everything above is held facts and is complete without it.
What would change this brief held, dated
- CISA KEV
- Not listed in the catalogue we hold. A listing changes this brief.
- exploit probability
- 0.00 on 2026-09-28 (FIRST's EPSS, a probability and not evidence of exploitation). Next band line: 10% (0.10). Crossing a line changes this brief.
- fix
- Held: 5.10.259; 5.15.210; 6.1.176; 6.6.143; 6.12.93; 6.18.35; 7.0.12; 7.1. A newer fix from the CNA or OSV changes this brief.
How to check this
Every value above is held with two dates: when it was true upstream (as_of) and when we recorded it (tx_from). Re-derive the exploit probability as it stood on any date:
SELECT value, source, source_version, as_of, tx_from
FROM volatile_valid_as_of('CVE-2026-63920', '2026-10-30T23:59:59.999999Z', now());