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Review reviewCritical

CVE-2026-63992

Linux

In the Linux kernel, the following vulnerability has been resolved: tunnels: do not assume transport header in iptunnel_pmtud_check_icmp() In some cases, iptunnel_pmtud_check_icmp() can be called while skb transport header is not set. This triggers an out-of-bound access, because (typeof(skb->transport_header))~0U is 65535. Access the icmp header based on IPv4 network header, after making sure icmp->type is present in skb linear part. Note that iptunnel_pmtud_check_icmpv6()) is fine.

CVSS
9.1
EPSS
-
- percentile
CISA KEV
Not listed
Published
2026.07.20
PRIORITY ASSESSMENT

Review review

The CVSS severity warrants an early asset and exposure review.

Known exploitationNot established by KEV
Exploit probability-
Technical severityCVSS 9.1

Vulnerability overview

In the Linux kernel, the following vulnerability has been resolved: tunnels: do not assume transport header in iptunnel_pmtud_check_icmp() In some cases, iptunnel_pmtud_check_icmp() can be called while skb transport header is not set. This triggers an out-of-bound access, because (typeof(skb->transport_header))~0U is 65535. Access the icmp header based on IPv4 network header, after making sure icmp->type is present in skb linear part. Note that iptunnel_pmtud_check_icmpv6()) is fine.

Affected product and versions

Product
Linux
Affected versions
>= 4cb47a8644cc9eb8ec81190a50e79e6530d0297f < 5a92cb45e34749865d03daf8d3500f77b5f6644c, >= 4cb47a8644cc9eb8ec81190a50e79e6530d0297f < c7b7ec3e69e673c0d6b57f74d21da50c485c598e, >= 4cb47a8644cc9eb8ec81190a50e79e6530d0297f < 7f4f7efe7f30edd29c4988de01728bf2398217e4, >= 4cb47a8644cc9eb8ec81190a50e79e6530d0297f < e917d0c69f01af2bb4fbea2b66d560a53b3ac7ec, >= 4cb47a8644cc9eb8ec81190a50e79e6530d0297f < a096b6e34f602950af9a2b0856cd93a5f4c276d7, >= 4cb47a8644cc9eb8ec81190a50e79e6530d0297f < 43368636c663cff6e59dde93cf4b8e43ac28eb93, >= 4cb47a8644cc9eb8ec81190a50e79e6530d0297f < cb549df9ce4ee15c9d5b19ddab12cf2128e4313c, >= 4cb47a8644cc9eb8ec81190a50e79e6530d0297f < 509323077ef79a26ba0c60bb556e45c12c398b2d, >= 5.9
Fixed versions
No verified fixed-version field is available yet

Recommended response sequence

Confirm exposure before applying a vendor-supported change.

Full remediation guide
  1. 1
    Identify

    Confirm that Linux and an affected version are present.

  2. 2
    Prioritize

    Combine exploitation signals with asset exposure and business criticality.

  3. 3
    Remediate

    Follow the vendor advisory or supported update path and preserve rollback options.

  4. 4
    Verify

    Recheck the version, service health, access paths, and relevant logs.

Technical data

CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H
CWE
Not available