CVE-2026-63993Network attack vector

Kernel memory corruption via stale VXLAN pointer

Published Jul 19, 2026 · Updated Jul 19, 2026

Use-after-free in Linux Kernel VXLAN transmit processing allows remote attackers to corrupt kernel memory via crafted bridged traffic. The VXLAN transmit path caches ip_hdr(skb) before skb_tunnel_check_pmtu(), which can reallocate skb->head, and later dereferences the stale old_iph pointer. Reachability requires an active VXLAN bridge port and attacker-controlled inner IP traffic; successful exploitation can crash or compromise the host kernel.

CVSS severity9.8
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

Use-after-free in Linux Kernel VXLAN transmit processing allows remote attackers to corrupt kernel memory via crafted bridged traffic. The VXLAN transmit path caches ip_hdr(skb) before skb_tunnel_check_pmtu(), which can reallocate skb->head, and later dereferences the stale old_iph pointer. Reachability requires an active VXLAN bridge port and attacker-controlled inner IP traffic; successful exploitation can crash or compromise the host kernel.

The record

CVE
CVE-2026-63993
Published
Jul 19, 2026
Updated
Jul 19, 2026
Vendor
The Linux Kernel Organization
Product
Linux Kernel
Classifications
T1210
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 <5303925e360527243b46a440a04667826bbc72b7
  2. Affected versionversion=4cb47a8644cc9eb8ec81190a50e79e6530d0297f <609e63312c29aad18026a1d3222e123d4b6b0feb
  3. Affected versionversion=4cb47a8644cc9eb8ec81190a50e79e6530d0297f <6b8bfce9d2f774d2c2243e0248e03efb99bba6c0
  4. Affected versionversion=4cb47a8644cc9eb8ec81190a50e79e6530d0297f <7d9ef0cb271555d8cf39fefe6c981e1493b25ecf
  5. Affected versionversion=4cb47a8644cc9eb8ec81190a50e79e6530d0297f <8d435d68d71fb875876b722f4136caf74f2f48bd
  6. Affected versionversion=4cb47a8644cc9eb8ec81190a50e79e6530d0297f <9257f56ac47ef1976bcd056cf986a9988eeec67a
  7. Affected versionversion=4cb47a8644cc9eb8ec81190a50e79e6530d0297f <a493efd4336cf19122ae0e4cbb3d31b32d70deea
  8. Affected versionversion=4cb47a8644cc9eb8ec81190a50e79e6530d0297f <dc3bfa050f873371e745bdf478b1f5b738e5733d
  9. Affected versionversion=5.9

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

The Linux Kernel Organization · Linux Kernelversion=4cb47a8644cc9eb8ec81190a50e79e6530d0297f <5303925e360527243b46a440a04667826bbc72b7; version=4cb47a8644cc9eb8ec81190a50e79e6530d0297f <609e63312c29aad18026a1d3222e123d4b6b0feb; version=4cb47a8644cc9eb8ec81190a50e79e6530d0297f <6b8bfce9d2f774d2c2243e0248e03efb99bba6c0; version=4cb47a8644cc9eb8ec81190a50e79e6530d0297f <7d9ef0cb271555d8cf39fefe6c981e1493b25ecf; version=4cb47a8644cc9eb8ec81190a50e79e6530d0297f <8d435d68d71fb875876b722f4136caf74f2f48bd; version=4cb47a8644cc9eb8ec81190a50e79e6530d0297f <9257f56ac47ef1976bcd056cf986a9988eeec67a; version=4cb47a8644cc9eb8ec81190a50e79e6530d0297f <a493efd4336cf19122ae0e4cbb3d31b32d70deea; version=4cb47a8644cc9eb8ec81190a50e79e6530d0297f <dc3bfa050f873371e745bdf478b1f5b738e5733d; version=5.9

Published CVSS scores

9.8Linux kernel CNACVSS:3.1/AV:N/AC:L/PR:N/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

T1210Exploitation of Remote Services

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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