CVE-2026-63994 - Vulnerability Details

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

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.

Published: 2026-07-19

Score: 9.8 Critical

EPSS: < 1% Very Low

KEV: No

Impact:

Action:

Analysis

Analysis and contextual insights are available on OpenCVE Cloud.

Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).

Vendor Product Default status Versions

Linux

unaffected

Version	Status	Constraints
`4cb47a8644cc9eb8ec81190a50e79e6530d0297f`	affected	< 95b6d772bfe788331d9742d73eaa12e113b2adc4
`4cb47a8644cc9eb8ec81190a50e79e6530d0297f`	affected	< 7254aef4d1a7e18e887af9010e2f2dc34806789b
`4cb47a8644cc9eb8ec81190a50e79e6530d0297f`	affected	< bf8b3f34c37c162357138e7c0942723b8b94fed1
`4cb47a8644cc9eb8ec81190a50e79e6530d0297f`	affected	< 76cd9398a0470257ab765bdf5f358a2af2e17934
`4cb47a8644cc9eb8ec81190a50e79e6530d0297f`	affected	< 50750d86a2e5266aba0c295483b3397843198b11
`4cb47a8644cc9eb8ec81190a50e79e6530d0297f`	affected	< 6dff77899b9e9fe5d854abda3a98ad04e7229ef7
`4cb47a8644cc9eb8ec81190a50e79e6530d0297f`	affected	< f3f204541f280a6ecb04503a0d6794d93990ca43
`4cb47a8644cc9eb8ec81190a50e79e6530d0297f`	affected	< b4bc94353050b1fa7b702bd4c6600710dd926cff

Linux

affected

Version	Status	Constraints
`5.9`	affected	—
`0`	unaffected	< 5.9
`5.10.259`	unaffected	≤ 5.10.*
`5.15.210`	unaffected	≤ 5.15.*
`6.1.176`	unaffected	≤ 6.1.*
`6.6.143`	unaffected	≤ 6.6.*
`6.12.93`	unaffected	≤ 6.12.*
`6.18.35`	unaffected	≤ 6.18.*
`7.0.12`	unaffected	≤ 7.0.*
`7.1`	unaffected	≤ *

No data.

Vendor Product Confidence Versions

Linux

Linux Kernel

99%

Version	Status	Scheme	Platform
`[4cb47a8644cc9eb8ec81190a50e79e6530d0297f,95b6d772bfe788331d9742d73eaa12e113b2adc4)`	affected	code_commit	—
`[4cb47a8644cc9eb8ec81190a50e79e6530d0297f,7254aef4d1a7e18e887af9010e2f2dc34806789b)`	affected	code_commit	—
`[4cb47a8644cc9eb8ec81190a50e79e6530d0297f,bf8b3f34c37c162357138e7c0942723b8b94fed1)`	affected	code_commit	—
`[4cb47a8644cc9eb8ec81190a50e79e6530d0297f,76cd9398a0470257ab765bdf5f358a2af2e17934)`	affected	code_commit	—
`[4cb47a8644cc9eb8ec81190a50e79e6530d0297f,50750d86a2e5266aba0c295483b3397843198b11)`	affected	code_commit	—
`[4cb47a8644cc9eb8ec81190a50e79e6530d0297f,6dff77899b9e9fe5d854abda3a98ad04e7229ef7)`	affected	code_commit	—
`[4cb47a8644cc9eb8ec81190a50e79e6530d0297f,f3f204541f280a6ecb04503a0d6794d93990ca43)`	affected	code_commit	—
`[4cb47a8644cc9eb8ec81190a50e79e6530d0297f,b4bc94353050b1fa7b702bd4c6600710dd926cff)`	affected	code_commit	—

Linux

Linux Kernel

99%

Version	Status	Scheme	Platform
`5.9`	affected	generic	—
`[0,5.9)`	unaffected	semver	—
`[5.10.259,5.11.0)`	unaffected	semver	—
`[5.15.210,5.16.0)`	unaffected	semver	—
`[6.1.176,6.2.0)`	unaffected	semver	—
`[6.6.143,6.7.0)`	unaffected	semver	—
`[6.12.93,6.13.0)`	unaffected	semver	—
`[6.18.35,6.19.0)`	unaffected	semver	—
`[7.0.12,7.1.0)`	unaffected	semver	—
`[7.1,*]`	unaffected	semver	—

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Remediation

No vendor fix or workaround currently provided.

Additional remediation guidance may be available on OpenCVE Cloud.

Tracking

Sign in to view the affected projects.

Advisories

No advisories yet.

No CVSS v4.0

Attack Vector Network

Attack Complexity Low

Privileges Required None

Scope Unchanged

Confidentiality Impact High

Integrity Impact High

Availability Impact High

User Interaction None

No CVSS v3.0

No CVSS v2

This CVE is not in the KEV list.

The EPSS score is 0.00521.

Key SSVC decision points have not yet been added.

References

Link	Providers
https://git.kernel.org/stable/c/50750d86a2e5266aba0c295483b3397843198b11
https://git.kernel.org/stable/c/6dff77899b9e9fe5d854abda3a98ad04e7229ef7
https://git.kernel.org/stable/c/7254aef4d1a7e18e887af9010e2f2dc34806789b
https://git.kernel.org/stable/c/76cd9398a0470257ab765bdf5f358a2af2e17934
https://git.kernel.org/stable/c/95b6d772bfe788331d9742d73eaa12e113b2adc4
https://git.kernel.org/stable/c/b4bc94353050b1fa7b702bd4c6600710dd926cff
https://git.kernel.org/stable/c/bf8b3f34c37c162357138e7c0942723b8b94fed1
https://git.kernel.org/stable/c/f3f204541f280a6ecb04503a0d6794d93990ca43

History

Mon, 20 Jul 2026 14:45:00 +0000

Type	Values Removed	Values Added
Metrics		cvssV3_1 `{'score': 9.8, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H'}`

Sun, 19 Jul 2026 15:30:00 +0000

Type	Values Removed	Values Added
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.
Title		tunnels: load network headers after skb_cow() in iptunnel_pmtud_build_icmp[v6]()
First Time appeared		Linux Linux linux Kernel
CPEs		cpe:2.3:o:linux:linux_kernel::::::::
Vendors & Products		Linux Linux linux Kernel
References		https://git.kernel.org/stable/c/50750d86a2e5266aba0c295483b3397843198b11 https://git.kernel.org/stable/c/6dff77899b9e9fe5d854abda3a98ad04e7229ef7 https://git.kernel.org/stable/c/7254aef4d1a7e18e887af9010e2f2dc34806789b https://git.kernel.org/stable/c/76cd9398a0470257ab765bdf5f358a2af2e17934 https://git.kernel.org/stable/c/95b6d772bfe788331d9742d73eaa12e113b2adc4 https://git.kernel.org/stable/c/b4bc94353050b1fa7b702bd4c6600710dd926cff https://git.kernel.org/stable/c/bf8b3f34c37c162357138e7c0942723b8b94fed1 https://git.kernel.org/stable/c/f3f204541f280a6ecb04503a0d6794d93990ca43

Subscriptions

Linux Linux Kernel

MITRE

Status: PUBLISHED

Assigner: Linux

Published: 2026-07-19T14:56:13.896Z

Updated: 2026-07-20T13:42:09.911Z

Reserved: 2026-07-19T07:54:57.026Z

Link: CVE-2026-63994

Vulnrichment

No data.

NVD

No data.

Redhat

No data.

OpenCVE Enrichment

Updated: 2026-07-21T06:45:02Z

Weaknesses

No weakness.

Tracking

Attack Vector Network

Attack Complexity Low

Privileges Required None

Scope Unchanged

Confidentiality Impact High

Integrity Impact High

Availability Impact High

User Interaction None

Subscriptions

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