Linux: Use After Free
CVE-2024-39463 is a high-severity use after free vulnerability in Linux, with a CVSS 3.1 base score of 7.8 out of 10. It can be exploited with local access to the system by an attacker with a low-privileged account, without any action from a user. The record lists versions 3bb6763a8319170c2d41c4232c8e7e4c37dcacfb, cb299cdba09f46f090b843d78ba26b667d50a456, f0c5c944c6d8614c19e6e9a97fd2011dcd30e8f5 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 0.25% chance of exploitation within 30 days, which is low compared with other CVEs.
High severity with no evidence of exploitation so far.
What to do
- Update Linux to 3bb6763a8319170c2d41c4232c8e7e4c37dcacfb or cb299cdba09f46f090b843d78ba26b667d50a456 or f0c5c944c6d8614c19e6e9a97fd2011dcd30e8f5 or fe17ebf22feb4ad7094d597526d558a49aac92b4, whichever matches your release line, or a later version.
- Update linux_kernel to cb299cdba09f or f0c5c944c6d8 or fe17ebf22feb or c898afdc1564, whichever matches your release line, or a later version.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Linux | Linux | 154372e67d4053e56591245eb413686621941333 up to, but not including, 3bb6763a8319170c2d41c4232c8e7e4c37dcacfb; 154372e67d4053e56591245eb413686621941333 up to, but not including, cb299cdba09f46f090b843d78ba26b667d50a456; 154372e67d4053e56591245eb413686621941333 up to, but not including, f0c5c944c6d8614c19e6e9a97fd2011dcd30e8f5; 154372e67d4053e56591245eb413686621941333 up to, but not including, fe17ebf22feb4ad7094d597526d558a49aac92b4; 154372e67d4053e56591245eb413686621941333 up to, but not including, c898afdc15645efb555acb6d85b484eb40a45409; 5.11 | 3bb6763a8319170c2d41c4232c8e7e4c37dcacfb, cb299cdba09f46f090b843d78ba26b667d50a456, f0c5c944c6d8614c19e6e9a97fd2011dcd30e8f5, fe17ebf22feb4ad7094d597526d558a49aac92b4, c898afdc15645efb555acb6d85b484eb40a45409 |
| Linux | linux_kernel | 5.11; 154372e67d40 up to, but not including, cb299cdba09f; 154372e67d40 up to, but not including, f0c5c944c6d8; 154372e67d40 up to, but not including, fe17ebf22feb; 154372e67d40 up to, but not including, c898afdc1564 | cb299cdba09f, f0c5c944c6d8, fe17ebf22feb, c898afdc1564 |
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
- LocalThe attacker needs local access or must trick a user into running something.
- Attack complexity
- LowNo special conditions are needed; the attack works reliably.
- Privileges required
- LowA basic user account is enough.
- 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:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H. Scored by NVD.
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 3.1 | 7.8 | High | NVD |
| CVSS 3.1 | 7.8 | High | CISA (ADP) |
Official description
In the Linux kernel, the following vulnerability has been resolved: 9p: add missing locking around taking dentry fid list Fix a use-after-free on dentry's d_fsdata fid list when a thread looks up a fid through dentry while another thread unlinks it: UAF thread: refcount_t: addition on 0; use-after-free. p9_fid_get linux/./include/net/9p/client.h:262 v9fs_fid_find+0x236/0x280 linux/fs/9p/fid.c:129 v9fs_fid_lookup_with_uid linux/fs/9p/fid.c:181 v9fs_fid_lookup+0xbf/0xc20 linux/fs/9p/fid.c:314 v9fs_vfs_getattr_dotl+0xf9/0x360 linux/fs/9p/vfs_inode_dotl.c:400 vfs_statx+0xdd/0x4d0 linux/fs/stat.c:248 Freed by: p9_fid_destroy (inlined) p9_client_clunk+0xb0/0xe0 linux/net/9p/client.c:1456 p9_fid_put linux/./include/net/9p/client.h:278 v9fs_dentry_release+0xb5/0x140 linux/fs/9p/vfs_dentry.c:55 v9fs_remove+0x38f/0x620 linux/fs/9p/vfs_inode.c:518 vfs_unlink+0x29a/0x810 linux/fs/namei.c:4335 The problem is that d_fsdata was not accessed under d_lock, because d_release() normally is only called once the dentry is otherwise no longer accessible but since we also call it explicitly in v9fs_remove that lock is required: move the hlist out of the dentry under lock then unref its fids once they are no longer accessible.
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: no, technical impact: total).
- Record last changed materially (score, affected products, status or references).
References
Patches and release notes
- git.kernel.org/stable/c/3bb6763a8319170c2d41c4232c8e7e4c37dcacfb
- git.kernel.org/stable/c/c898afdc15645efb555acb6d85b484eb40a45409
- git.kernel.org/stable/c/cb299cdba09f46f090b843d78ba26b667d50a456
- git.kernel.org/stable/c/f0c5c944c6d8614c19e6e9a97fd2011dcd30e8f5
- git.kernel.org/stable/c/fe17ebf22feb4ad7094d597526d558a49aac92b4
Third-party and government advisories
- zerodayinitiative.com/advisories/ZDI-24-1194/Third Party Advisory
Recent Use After Free vulnerabilities
- 7.8 High severity
- 7.8 High severity
- 7.8 High severity
- 7.8 High severity
- 8.8 High severity
- 8.8 High severity
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