How severe is CVE-2026-63992?

CVE-2026-63992 has a CVSS score of 9.1/10, rated CRITICAL. Immediate patching is strongly recommended.

Which packages are affected by CVE-2026-63992?

CVE-2026-63992 affects the following packages: Kernel (Linux). Ecosystems affected: Linux.

How do I fix CVE-2026-63992?

Update Kernel to 5.10.259 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-63992 is resolved across your whole dependency graph.

How do I detect CVE-2026-63992 in my Linux dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for Kernel. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.

How do I mitigate CVE-2026-63992 if there is no patch (or I can't update yet)?

If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

How does O3 Security protect against CVE-2026-63992?

O3 pinpoints whether CVE-2026-63992 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.

Is CVE-2026-63992 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-63992 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2026-63992?

CVE-2026-63992 has an EPSS (Exploit Prediction Scoring System) score of 0.5%, placing it in the 41th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

When was CVE-2026-63992 published, and has it been updated?

CVE-2026-63992 was published on July 19, 2026 and was last updated on July 22, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🐧 Linux

CVE-2026-63992

CRITICAL

tunnels: do not assume transport header in iptunnel_pmtud_check_icmp()

Published

Jul 19, 2026

Updated

Jul 22, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

EPSS Exploitation Probability

via FIRST.org ↗

0.5%probability of exploitation in next 30 days

Lower Risk41th percentile0.00%

EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.

Blast Radius

1 pkg affected

🐧Kernel

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Linux packages — download data is not available via public APIs for these ecosystems.

Description

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 Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
🐧Linux	`Kernel`	≥ 5.9.0&&< 5.10.259	5.10.259

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for Kernel. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update Kernel to 5.10.259 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-63992 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether CVE-2026-63992 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.

Tailored to CVE-2026-63992. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.

Frequently Asked Questions

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.

O3 Security · Impact-Aware SCA

Is CVE-2026-63992 in your dependencies?

O3 detects CVE-2026-63992 across Linux dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.

Scan my dependencies How O3 SCA works