Linux: Use After Free
CVE-2026-63994 is a critical-severity use after free vulnerability in Linux, with a CVSS 3.1 base score of 9.8 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. The record lists versions 95b6d772bfe788331d9742d73eaa12e113b2adc4, 7254aef4d1a7e18e887af9010e2f2dc34806789b, bf8b3f34c37c162357138e7c0942723b8b94fed1 as the first without the flaw, so updating Linux to one of those releases or later removes the exposure. There is no confirmed exploitation so far. EPSS estimates a 0.51% chance of exploitation within 30 days, which is low compared with other CVEs.
Critical severity: a successful attack would have severe impact.
What to do
- Update Linux to 95b6d772bfe788331d9742d73eaa12e113b2adc4 or 7254aef4d1a7e18e887af9010e2f2dc34806789b or bf8b3f34c37c162357138e7c0942723b8b94fed1 or 76cd9398a0470257ab765bdf5f358a2af2e17934, whichever matches your release line, or a later version.
- Update Linux Kernel to 5.10.259 or 5.15.210 or 6.1.176 or 6.6.143, whichever matches your release line, or a later version.
- Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Linux | Linux | 4cb47a8644cc9eb8ec81190a50e79e6530d0297f up to, but not including, 95b6d772bfe788331d9742d73eaa12e113b2adc4; 4cb47a8644cc9eb8ec81190a50e79e6530d0297f up to, but not including, 7254aef4d1a7e18e887af9010e2f2dc34806789b; 4cb47a8644cc9eb8ec81190a50e79e6530d0297f up to, but not including, bf8b3f34c37c162357138e7c0942723b8b94fed1; 4cb47a8644cc9eb8ec81190a50e79e6530d0297f up to, but not including, 76cd9398a0470257ab765bdf5f358a2af2e17934; 4cb47a8644cc9eb8ec81190a50e79e6530d0297f up to, but not including, 50750d86a2e5266aba0c295483b3397843198b11; 4cb47a8644cc9eb8ec81190a50e79e6530d0297f up to, but not including, 6dff77899b9e9fe5d854abda3a98ad04e7229ef7; 4cb47a8644cc9eb8ec81190a50e79e6530d0297f up to, but not including, f3f204541f280a6ecb04503a0d6794d93990ca43; 4cb47a8644cc9eb8ec81190a50e79e6530d0297f up to, but not including, b4bc94353050b1fa7b702bd4c6600710dd926cff; and 1 more ranges | 95b6d772bfe788331d9742d73eaa12e113b2adc4, 7254aef4d1a7e18e887af9010e2f2dc34806789b, bf8b3f34c37c162357138e7c0942723b8b94fed1, 76cd9398a0470257ab765bdf5f358a2af2e17934, 50750d86a2e5266aba0c295483b3397843198b11, 6dff77899b9e9fe5d854abda3a98ad04e7229ef7 |
| Linux | Linux Kernel | 5.9 up to, but not including, 5.10.259; 5.11 up to, but not including, 5.15.210; 5.16 up to, but not including, 6.1.176; 6.2 up to, but not including, 6.6.143; 6.7 up to, but not including, 6.12.93; 6.13 up to, but not including, 6.18.35; 6.19 up to, but not including, 7.0.12; 7.1 | 5.10.259, 5.15.210, 6.1.176, 6.6.143, 6.12.93, 6.18.35 |
Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- NetworkCan be exploited remotely over a network, including the internet.
- Attack complexity
- LowNo special conditions are needed; the attack works reliably.
- Privileges required
- NoneNo account or login is needed.
- User interaction
- NoneNo action by a victim is required.
- Scope
- UnchangedImpact stays within the vulnerable component.
- Confidentiality
- HighAll data handled by the component can be read.
- Integrity
- HighData or code can be modified at will.
- Availability
- HighThe component can be taken down completely.
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H. Scored by CNA.
Official description
In the Linux kernel, the following vulnerability has been resolved: tunnels: load network headers after skb_cow() in iptunnel_pmtud_build_icmp[v6]() Sashiko found that iptunnel_pmtud_build_icmp() and iptunnel_pmtud_build_icmpv6() were caching ip_hdr() and ipv6_hdr() before an skb_cow() call which can reallocate skb->head. Fix this possible UAF by initializing the local variables after the skb_cow() call. Remove skb_reset_network_header() calls which were not needed.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Use After Free
The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory belongs to the code that operates on the new pointer.
How developers prevent this class of flaw
- Choose a language that provides automatic memory management.
- When freeing pointers, be sure to set them to NULL once they are freed. However, the utilization of multiple or complex data structures may lower the usefulness of this strategy.
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: none, automatable: yes, technical impact: total).
- Record last changed materially (score, affected products, status or references).
References
Patches and release notes
- git.kernel.org/stable/c/50750d86a2e5266aba0c295483b3397843198b11
- git.kernel.org/stable/c/6dff77899b9e9fe5d854abda3a98ad04e7229ef7
- git.kernel.org/stable/c/7254aef4d1a7e18e887af9010e2f2dc34806789b
- git.kernel.org/stable/c/76cd9398a0470257ab765bdf5f358a2af2e17934
- git.kernel.org/stable/c/95b6d772bfe788331d9742d73eaa12e113b2adc4
- git.kernel.org/stable/c/b4bc94353050b1fa7b702bd4c6600710dd926cff
- git.kernel.org/stable/c/bf8b3f34c37c162357138e7c0942723b8b94fed1
- git.kernel.org/stable/c/f3f204541f280a6ecb04503a0d6794d93990ca43
Recent Use After Free vulnerabilities
- 8.8 High severity
- 9.8 Critical severity
- 9.8 Critical severity
- 7.8 High severity
- 9.8 Critical severity
- 8.8 High severity
Spotted an error? Tell us.