CVE-2026-63994: tunnels: load network headers after skb_cow() in iptunnel_pmtud_build_icmp[v6]()

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

• linux linux kernel5.9 and later · before 5.10.259
• linux linux kernel5.11 and later · before 5.15.210
• linux linux kernel5.16 and later · before 6.1.176
• linux linux kernel6.2 and later · before 6.6.143
• linux linux kernel6.7 and later · before 6.12.93
• linux linux kernel6.13 and later · before 6.18.35
• linux linux kernel6.19 and later · before 7.0.12
• linux linux kernel7.1

Versions reported by the vendor

Affected version ranges reported by the assigning authority (Linux). Independent of NVD's CPE analysis and usually ahead of it.

• Linux Linux

  • 5.9affected
  • 4cb47a8644cc9eb8ec81190a50e79e6530d0297f and later · before 95b6d772bfe788331d9742d73eaa12e113b2adc4affected · git
  • 4cb47a8644cc9eb8ec81190a50e79e6530d0297f and later · before 7254aef4d1a7e18e887af9010e2f2dc34806789baffected · git
  • 4cb47a8644cc9eb8ec81190a50e79e6530d0297f and later · before bf8b3f34c37c162357138e7c0942723b8b94fed1affected · git
  • 4cb47a8644cc9eb8ec81190a50e79e6530d0297f and later · before 76cd9398a0470257ab765bdf5f358a2af2e17934affected · git
  • 4cb47a8644cc9eb8ec81190a50e79e6530d0297f and later · before 50750d86a2e5266aba0c295483b3397843198b11affected · git
  • 4cb47a8644cc9eb8ec81190a50e79e6530d0297f and later · before 6dff77899b9e9fe5d854abda3a98ad04e7229ef7affected · git
  • 4cb47a8644cc9eb8ec81190a50e79e6530d0297f and later · before f3f204541f280a6ecb04503a0d6794d93990ca43affected · git
  • 4cb47a8644cc9eb8ec81190a50e79e6530d0297f and later · before b4bc94353050b1fa7b702bd4c6600710dd926cffaffected · git
  • before 5.9not affected · semver

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

Other highest-scoring records for the same primary product.

• CVE-2026-31431crypto: algif_aead - Revert to operating out-of-placeKEV
  90Now
• CVE-2022-0847A flaw was found in the way the "flags" member of the new pipe buffer structure was lacking proper initialization in copy_page_to_iter_pipe KEV
  89Now
• CVE-2021-22555Heap Out-Of-Bounds Write in Netfilter IP6T_SO_SET_REPLACEKEV
  85Now

Published before and after this one in the same product

• ← EarlierCVE-2026-63992Jul 19, 2026 · tunnels: do not assume transport header in iptunnel_pmtud_check_icmp()
  36Monitor
• ← EarlierCVE-2026-63993Jul 19, 2026 · vxlan: do not reuse cached ip_hdr() value after skb_tunnel_check_pmtu()
  39Monitor
• Later →CVE-2026-63995Jul 19, 2026 · ethtool: cmis: validate start_cmd_payload_size from module
  31Monitor

FIRST EPSS daily score; only changes of 0.01 or more are recorded (step chart).

Root cause

After a memory region is freed, another reference pointing to it is still used. By then, the same region may have been allocated for different data.

A representative example of this vulnerability class. Not the vendor's source code; it shows the faulty pattern and its fix.

1free(dev->buf);2/* ... another thread is still running ... */3process(dev->buf);

1lock(&dev->lock);2free(dev->buf);3dev->buf = NULL;4unlock(&dev->lock);

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

MITRE has no CAPEC/ATT&CK mapping for this CWE.