CVE-2026-63994
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.
INFO
Published Date :
July 19, 2026, 4:17 p.m.
Last Modified :
July 30, 2026, 2:51 p.m.
Remotely Exploit :
Yes !
Source :
416baaa9-dc9f-4396-8d5f-8c081fb06d67
CVSS Scores
| Score | Version | Severity | Vector | Exploitability Score | Impact Score | Source |
|---|---|---|---|---|---|---|
| CVSS 3.1 | CRITICAL | 416baaa9-dc9f-4396-8d5f-8c081fb06d67 |
Solution
- Reinitialize local header variables after skb_cow() call.
- Remove unneeded skb_reset_network_header() calls.
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2026-63994.
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2026-63994 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2026-63994
weaknesses.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
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The following list is the news that have been mention
CVE-2026-63994 vulnerability anywhere in the article.
The following table lists the changes that have been made to the
CVE-2026-63994 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
-
CVE Modified by 416baaa9-dc9f-4396-8d5f-8c081fb06d67
Jul. 20, 2026
Action Type Old Value New Value Added CVSS V3.1 AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H -
New CVE Received by 416baaa9-dc9f-4396-8d5f-8c081fb06d67
Jul. 19, 2026
Action Type Old Value New Value Added Affected [{'repo': 'https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git', 'vendor': 'Linux', 'product': 'Linux', 'versions': [{'status': 'affected', 'version': '4cb47a8644cc9eb8ec81190a50e79e6530d0297f', 'lessThan': '95b6d772bfe788331d9742d73eaa12e113b2adc4', 'versionType': 'git'}, {'status': 'affected', 'version': '4cb47a8644cc9eb8ec81190a50e79e6530d0297f', 'lessThan': '7254aef4d1a7e18e887af9010e2f2dc34806789b', 'versionType': 'git'}, {'status': 'affected', 'version': '4cb47a8644cc9eb8ec81190a50e79e6530d0297f', 'lessThan': 'bf8b3f34c37c162357138e7c0942723b8b94fed1', 'versionType': 'git'}, {'status': 'affected', 'version': '4cb47a8644cc9eb8ec81190a50e79e6530d0297f', 'lessThan': '76cd9398a0470257ab765bdf5f358a2af2e17934', 'versionType': 'git'}, {'status': 'affected', 'version': '4cb47a8644cc9eb8ec81190a50e79e6530d0297f', 'lessThan': '50750d86a2e5266aba0c295483b3397843198b11', 'versionType': 'git'}, {'status': 'affected', 'version': '4cb47a8644cc9eb8ec81190a50e79e6530d0297f', 'lessThan': '6dff77899b9e9fe5d854abda3a98ad04e7229ef7', 'versionType': 'git'}, {'status': 'affected', 'version': '4cb47a8644cc9eb8ec81190a50e79e6530d0297f', 'lessThan': 'f3f204541f280a6ecb04503a0d6794d93990ca43', 'versionType': 'git'}, {'status': 'affected', 'version': '4cb47a8644cc9eb8ec81190a50e79e6530d0297f', 'lessThan': 'b4bc94353050b1fa7b702bd4c6600710dd926cff', 'versionType': 'git'}], 'programFiles': ['net/ipv4/ip_tunnel_core.c'], 'defaultStatus': 'unaffected'}, {'repo': 'https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git', 'vendor': 'Linux', 'product': 'Linux', 'versions': [{'status': 'affected', 'version': '5.9'}, {'status': 'unaffected', 'version': '0', 'lessThan': '5.9', 'versionType': 'semver'}, {'status': 'unaffected', 'version': '5.10.259', 'versionType': 'semver', 'lessThanOrEqual': '5.10.*'}, {'status': 'unaffected', 'version': '5.15.210', 'versionType': 'semver', 'lessThanOrEqual': '5.15.*'}, {'status': 'unaffected', 'version': '6.1.176', 'versionType': 'semver', 'lessThanOrEqual': '6.1.*'}, {'status': 'unaffected', 'version': '6.6.143', 'versionType': 'semver', 'lessThanOrEqual': '6.6.*'}, {'status': 'unaffected', 'version': '6.12.93', 'versionType': 'semver', 'lessThanOrEqual': '6.12.*'}, {'status': 'unaffected', 'version': '6.18.35', 'versionType': 'semver', 'lessThanOrEqual': '6.18.*'}, {'status': 'unaffected', 'version': '7.0.12', 'versionType': 'semver', 'lessThanOrEqual': '7.0.*'}, {'status': 'unaffected', 'version': '7.1', 'versionType': 'original_commit_for_fix', 'lessThanOrEqual': '*'}], 'programFiles': ['net/ipv4/ip_tunnel_core.c'], 'defaultStatus': 'affected'}] 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. Added Reference https://git.kernel.org/stable/c/50750d86a2e5266aba0c295483b3397843198b11 Added Reference https://git.kernel.org/stable/c/6dff77899b9e9fe5d854abda3a98ad04e7229ef7 Added Reference https://git.kernel.org/stable/c/7254aef4d1a7e18e887af9010e2f2dc34806789b Added Reference https://git.kernel.org/stable/c/76cd9398a0470257ab765bdf5f358a2af2e17934 Added Reference https://git.kernel.org/stable/c/95b6d772bfe788331d9742d73eaa12e113b2adc4 Added Reference https://git.kernel.org/stable/c/b4bc94353050b1fa7b702bd4c6600710dd926cff Added Reference https://git.kernel.org/stable/c/bf8b3f34c37c162357138e7c0942723b8b94fed1 Added Reference https://git.kernel.org/stable/c/f3f204541f280a6ecb04503a0d6794d93990ca43