Linux: Use After Free
CVE-2024-26737 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 5268bb02107b9eedfdcd51db75b407d10043368c, addf5e297e6cbf5341f9c07720693ca9ba0057b5, 8327ed12e8ebc5436bfaa1786c49988894f9c8a6 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 5268bb02107b9eedfdcd51db75b407d10043368c or addf5e297e6cbf5341f9c07720693ca9ba0057b5 or 8327ed12e8ebc5436bfaa1786c49988894f9c8a6 or 7d80a9e745fa5b47da3bca001f186c02485c7c33, whichever matches your release line, or a later version.
- Update Linux Kernel to 5.15.150 or 6.1.80 or 6.6.19 or 6.7.7, whichever matches your release line, or a later version.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Linux | Linux | b00628b1c7d595ae5b544e059c27b1f5828314b4 up to, but not including, 5268bb02107b9eedfdcd51db75b407d10043368c; b00628b1c7d595ae5b544e059c27b1f5828314b4 up to, but not including, addf5e297e6cbf5341f9c07720693ca9ba0057b5; b00628b1c7d595ae5b544e059c27b1f5828314b4 up to, but not including, 8327ed12e8ebc5436bfaa1786c49988894f9c8a6; b00628b1c7d595ae5b544e059c27b1f5828314b4 up to, but not including, 7d80a9e745fa5b47da3bca001f186c02485c7c33; b00628b1c7d595ae5b544e059c27b1f5828314b4 up to, but not including, 0281b919e175bb9c3128bd3872ac2903e9436e3f; 5.15 | 5268bb02107b9eedfdcd51db75b407d10043368c, addf5e297e6cbf5341f9c07720693ca9ba0057b5, 8327ed12e8ebc5436bfaa1786c49988894f9c8a6, 7d80a9e745fa5b47da3bca001f186c02485c7c33, 0281b919e175bb9c3128bd3872ac2903e9436e3f |
| Linux | Linux Kernel | 5.15 up to, but not including, 5.15.150; 5.16 up to, but not including, 6.1.80; 6.2 up to, but not including, 6.6.19; 6.7 up to, but not including, 6.7.7; 6.8 | 5.15.150, 6.1.80, 6.6.19, 6.7.7 |
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 CNA.
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 3.1 | 7.8 | High | CNA |
| CVSS 3.1 | 5.5 | Medium | CISA (ADP) |
Official description
In the Linux kernel, the following vulnerability has been resolved: bpf: Fix racing between bpf_timer_cancel_and_free and bpf_timer_cancel The following race is possible between bpf_timer_cancel_and_free and bpf_timer_cancel. It will lead a UAF on the timer->timer. bpf_timer_cancel(); spin_lock(); t = timer->time; spin_unlock(); bpf_timer_cancel_and_free(); spin_lock(); t = timer->timer; timer->timer = NULL; spin_unlock(); hrtimer_cancel(&t->timer); kfree(t); /* UAF on t */ hrtimer_cancel(&t->timer); In bpf_timer_cancel_and_free, this patch frees the timer->timer after a rcu grace period. This requires a rcu_head addition to the "struct bpf_hrtimer". Another kfree(t) happens in bpf_timer_init, this does not need a kfree_rcu because it is still under the spin_lock and timer->timer has not been visible by others yet. In bpf_timer_cancel, rcu_read_lock() is added because this helper can be used in a non rcu critical section context (e.g. from a sleepable bpf prog). Other timer->timer usages in helpers.c have been audited, bpf_timer_cancel() is the only place where timer->timer is used outside of the spin_lock. Another solution considered is to mark a t->flag in bpf_timer_cancel and clear it after hrtimer_cancel() is done. In bpf_timer_cancel_and_free, it busy waits for the flag to be cleared before kfree(t). This patch goes with a straight forward solution and frees timer->timer after a rcu grace period.
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: partial).
- Record last changed materially (score, affected products, status or references).
References
Patches and release notes
- git.kernel.org/stable/c/0281b919e175bb9c3128bd3872ac2903e9436e3f
- git.kernel.org/stable/c/5268bb02107b9eedfdcd51db75b407d10043368c
- git.kernel.org/stable/c/7d80a9e745fa5b47da3bca001f186c02485c7c33
- git.kernel.org/stable/c/8327ed12e8ebc5436bfaa1786c49988894f9c8a6
- git.kernel.org/stable/c/addf5e297e6cbf5341f9c07720693ca9ba0057b5
Recent Use After Free vulnerabilities
- 7.8 High severity
- 7.8 High severity
- 7.8 High severity
- 7.8 High severity
- 7.8 High severity
- 7.8 High severity
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