CVE-2026-63994

tunnels: load network headers after skb_cow() in iptunnel_pmtud_build_icmp[v6]()

State: Published
Severity: 9.8 Critical
Published: Jul 19, 2026
Updated: Oct 19, 2026
Reserved: Jul 19, 2026

Description

In the Linux kernel, the following vulnerability has been resolved:

tunnels: load network headers after skb_cow() in iptunnel_pmtud_build_icmp[v6]()

Sashiko found that iptunnel_pmtud_build_icmp() and iptunnel_pmtud_build_icmpv6() were caching ip_hdr() and ipv6_hdr() before an skb_cow() call which can reallocate skb->head.

Fix this possible UAF by initializing the local variables after the skb_cow() call.

Remove skb_reset_network_header() calls which were not needed.

Scores

CVSS	Score	Vector	Source
3.1	9.8 Critical	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H	Linux

Weaknesses

CWE-416 Use After Free

Affected Products

Product	Versions
LinuxLinux	4cb47a8644cc9eb8ec81190a50e79e6530d0297f to before 95b6d772bfe788331d9742d73eaa12e113b2adc4Affected 4cb47a8644cc9eb8ec81190a50e79e6530d0297f to before 7254aef4d1a7e18e887af9010e2f2dc34806789bAffected 4cb47a8644cc9eb8ec81190a50e79e6530d0297f to before bf8b3f34c37c162357138e7c0942723b8b94fed1Affected 4cb47a8644cc9eb8ec81190a50e79e6530d0297f to before 76cd9398a0470257ab765bdf5f358a2af2e17934Affected 4cb47a8644cc9eb8ec81190a50e79e6530d0297f to before 50750d86a2e5266aba0c295483b3397843198b11Affected 4cb47a8644cc9eb8ec81190a50e79e6530d0297f to before 6dff77899b9e9fe5d854abda3a98ad04e7229ef7Affected 4cb47a8644cc9eb8ec81190a50e79e6530d0297f to before f3f204541f280a6ecb04503a0d6794d93990ca43Affected 4cb47a8644cc9eb8ec81190a50e79e6530d0297f to before b4bc94353050b1fa7b702bd4c6600710dd926cffAffected
LinuxLinux	5.9Affected before 5.9Not affected 5.10.259 through 5.10.Not affected 5.15.210 through 5.15.Not affected 6.1.176 through 6.1.Not affected 6.6.143 through 6.6.Not affected 6.12.93 through 6.12.Not affected 6.18.35 through 6.18.Not affected 7.0.12 through 7.0.*Not affected 7.1 and laterNot affected

Product

Versions

LinuxLinux

4cb47a8644cc9eb8ec81190a50e79e6530d0297f to before 95b6d772bfe788331d9742d73eaa12e113b2adc4Affected
4cb47a8644cc9eb8ec81190a50e79e6530d0297f to before 7254aef4d1a7e18e887af9010e2f2dc34806789bAffected
4cb47a8644cc9eb8ec81190a50e79e6530d0297f to before bf8b3f34c37c162357138e7c0942723b8b94fed1Affected
4cb47a8644cc9eb8ec81190a50e79e6530d0297f to before 76cd9398a0470257ab765bdf5f358a2af2e17934Affected
4cb47a8644cc9eb8ec81190a50e79e6530d0297f to before 50750d86a2e5266aba0c295483b3397843198b11Affected
4cb47a8644cc9eb8ec81190a50e79e6530d0297f to before 6dff77899b9e9fe5d854abda3a98ad04e7229ef7Affected
4cb47a8644cc9eb8ec81190a50e79e6530d0297f to before f3f204541f280a6ecb04503a0d6794d93990ca43Affected
4cb47a8644cc9eb8ec81190a50e79e6530d0297f to before b4bc94353050b1fa7b702bd4c6600710dd926cffAffected

LinuxLinux

5.9Affected
before 5.9Not affected
5.10.259 through 5.10.*Not affected
5.15.210 through 5.15.*Not affected
6.1.176 through 6.1.*Not affected
6.6.143 through 6.6.*Not affected
6.12.93 through 6.12.*Not affected
6.18.35 through 6.18.*Not affected
7.0.12 through 7.0.*Not affected
7.1 and laterNot affected

References

Every record here comes from the CVE Program’s CVE List. © 1999–2026 The MITRE Corporation. CVE is a registered trademark of The MITRE Corporation. The records are reproduced under the CVE Program terms of use.