CVE-2026-63992Network attack vector

Kernel data disclosure and panic via unset header

Published Jul 19, 2026 · Updated Jul 19, 2026

Out-of-bounds read in Linux kernel IPv4 tunnels allows remote attackers to disclose kernel data or panic hosts via ICMP traffic. iptunnel_pmtud_check_icmp() interprets an unset skb transport-header offset as 65535 and reads beyond the ICMP header instead of using the validated IPv4 network header. The IPv4 tunnel PMTU path must process the packet; the IPv6 helper is unaffected, and the read exposes kernel memory or stops the system.

CVSS severity9.1
Critical
EPSS probability0.51%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Out-of-bounds read in Linux kernel IPv4 tunnels allows remote attackers to disclose kernel data or panic hosts via ICMP traffic. iptunnel_pmtud_check_icmp() interprets an unset skb transport-header offset as 65535 and reads beyond the ICMP header instead of using the validated IPv4 network header. The IPv4 tunnel PMTU path must process the packet; the IPv6 helper is unaffected, and the read exposes kernel memory or stops the system.

The record

CVE
CVE-2026-63992
Published
Jul 19, 2026
Updated
Jul 19, 2026
Vendor
The Linux Kernel Organization
Product
Linux Kernel
Classifications
CWE-805, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jul 19, 2026CVE publishedPublication date reported by the CVE source.
  2. Jul 19, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=4cb47a8644cc9eb8ec81190a50e79e6530d0297f <43368636c663cff6e59dde93cf4b8e43ac28eb93
  2. Affected versionversion=4cb47a8644cc9eb8ec81190a50e79e6530d0297f <509323077ef79a26ba0c60bb556e45c12c398b2d
  3. Affected versionversion=4cb47a8644cc9eb8ec81190a50e79e6530d0297f <5a92cb45e34749865d03daf8d3500f77b5f6644c
  4. Affected versionversion=4cb47a8644cc9eb8ec81190a50e79e6530d0297f <7f4f7efe7f30edd29c4988de01728bf2398217e4
  5. Affected versionversion=4cb47a8644cc9eb8ec81190a50e79e6530d0297f <a096b6e34f602950af9a2b0856cd93a5f4c276d7
  6. Affected versionversion=4cb47a8644cc9eb8ec81190a50e79e6530d0297f <c7b7ec3e69e673c0d6b57f74d21da50c485c598e
  7. Affected versionversion=4cb47a8644cc9eb8ec81190a50e79e6530d0297f <cb549df9ce4ee15c9d5b19ddab12cf2128e4313c
  8. Affected versionversion=4cb47a8644cc9eb8ec81190a50e79e6530d0297f <e917d0c69f01af2bb4fbea2b66d560a53b3ac7ec
  9. Affected versionversion=5.9

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

The Linux Kernel Organization · Linux Kernelversion=4cb47a8644cc9eb8ec81190a50e79e6530d0297f <43368636c663cff6e59dde93cf4b8e43ac28eb93; version=4cb47a8644cc9eb8ec81190a50e79e6530d0297f <509323077ef79a26ba0c60bb556e45c12c398b2d; version=4cb47a8644cc9eb8ec81190a50e79e6530d0297f <5a92cb45e34749865d03daf8d3500f77b5f6644c; version=4cb47a8644cc9eb8ec81190a50e79e6530d0297f <7f4f7efe7f30edd29c4988de01728bf2398217e4; version=4cb47a8644cc9eb8ec81190a50e79e6530d0297f <a096b6e34f602950af9a2b0856cd93a5f4c276d7; version=4cb47a8644cc9eb8ec81190a50e79e6530d0297f <c7b7ec3e69e673c0d6b57f74d21da50c485c598e; version=4cb47a8644cc9eb8ec81190a50e79e6530d0297f <cb549df9ce4ee15c9d5b19ddab12cf2128e4313c; version=4cb47a8644cc9eb8ec81190a50e79e6530d0297f <e917d0c69f01af2bb4fbea2b66d560a53b3ac7ec; version=5.9

Published CVSS scores

9.1LinuxCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H
7.0Red HatCVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-805Buffer Access with Incorrect Length Value
T1499.004Application or System Exploitation

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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