Linux: Use After Free
CVE-2026-63993 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 6b8bfce9d2f774d2c2243e0248e03efb99bba6c0, 9257f56ac47ef1976bcd056cf986a9988eeec67a, 8d435d68d71fb875876b722f4136caf74f2f48bd 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 6b8bfce9d2f774d2c2243e0248e03efb99bba6c0 or 9257f56ac47ef1976bcd056cf986a9988eeec67a or 8d435d68d71fb875876b722f4136caf74f2f48bd or dc3bfa050f873371e745bdf478b1f5b738e5733d, 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, 6b8bfce9d2f774d2c2243e0248e03efb99bba6c0; 4cb47a8644cc9eb8ec81190a50e79e6530d0297f up to, but not including, 9257f56ac47ef1976bcd056cf986a9988eeec67a; 4cb47a8644cc9eb8ec81190a50e79e6530d0297f up to, but not including, 8d435d68d71fb875876b722f4136caf74f2f48bd; 4cb47a8644cc9eb8ec81190a50e79e6530d0297f up to, but not including, dc3bfa050f873371e745bdf478b1f5b738e5733d; 4cb47a8644cc9eb8ec81190a50e79e6530d0297f up to, but not including, 609e63312c29aad18026a1d3222e123d4b6b0feb; 4cb47a8644cc9eb8ec81190a50e79e6530d0297f up to, but not including, 5303925e360527243b46a440a04667826bbc72b7; 4cb47a8644cc9eb8ec81190a50e79e6530d0297f up to, but not including, a493efd4336cf19122ae0e4cbb3d31b32d70deea; 4cb47a8644cc9eb8ec81190a50e79e6530d0297f up to, but not including, 7d9ef0cb271555d8cf39fefe6c981e1493b25ecf; and 1 more ranges | 6b8bfce9d2f774d2c2243e0248e03efb99bba6c0, 9257f56ac47ef1976bcd056cf986a9988eeec67a, 8d435d68d71fb875876b722f4136caf74f2f48bd, dc3bfa050f873371e745bdf478b1f5b738e5733d, 609e63312c29aad18026a1d3222e123d4b6b0feb, 5303925e360527243b46a440a04667826bbc72b7 |
| 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: vxlan: do not reuse cached ip_hdr() value after skb_tunnel_check_pmtu() skb_tunnel_check_pmtu() can change skb->head. Reusing old_iph afer skb_tunnel_check_pmtu() can cause an UAF. Use instead ip_hdr(skb) as done in drivers/net/bareudp.c and drivers/net/geneve.c. Found by Sashiko.
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/5303925e360527243b46a440a04667826bbc72b7
- git.kernel.org/stable/c/609e63312c29aad18026a1d3222e123d4b6b0feb
- git.kernel.org/stable/c/6b8bfce9d2f774d2c2243e0248e03efb99bba6c0
- git.kernel.org/stable/c/7d9ef0cb271555d8cf39fefe6c981e1493b25ecf
- git.kernel.org/stable/c/8d435d68d71fb875876b722f4136caf74f2f48bd
- git.kernel.org/stable/c/9257f56ac47ef1976bcd056cf986a9988eeec67a
- git.kernel.org/stable/c/a493efd4336cf19122ae0e4cbb3d31b32d70deea
- git.kernel.org/stable/c/dc3bfa050f873371e745bdf478b1f5b738e5733d
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
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