Linux: Use After Free
CVE-2024-26958 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 6cd3f13aaa62970b5169d990e936b2e96943bc6a, 4595d90b5d2ea5fa4d318d13f59055aa4bf3e7f5, 80d24b308b7ee7037fc90d8ac99f6f78df0a256f 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 6cd3f13aaa62970b5169d990e936b2e96943bc6a or 4595d90b5d2ea5fa4d318d13f59055aa4bf3e7f5 or 80d24b308b7ee7037fc90d8ac99f6f78df0a256f or 3abc2d160ed8213948b147295d77d44a22c88fa3, whichever matches your release line, or a later version.
- Update SIMATIC S7-1500 TM MFP - GNU/Linux subsystem to V1.1.1 or a later version.
- Update Linux Kernel to 5.10.215 or 5.15.154 or 6.1.84 or 6.6.24, whichever matches your release line, or a later version.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Linux | Linux | af7cf057933f01dc7f33ddfb5e436ad598ed17ad up to, but not including, 6cd3f13aaa62970b5169d990e936b2e96943bc6a; af7cf057933f01dc7f33ddfb5e436ad598ed17ad up to, but not including, 4595d90b5d2ea5fa4d318d13f59055aa4bf3e7f5; af7cf057933f01dc7f33ddfb5e436ad598ed17ad up to, but not including, 80d24b308b7ee7037fc90d8ac99f6f78df0a256f; af7cf057933f01dc7f33ddfb5e436ad598ed17ad up to, but not including, 3abc2d160ed8213948b147295d77d44a22c88fa3; af7cf057933f01dc7f33ddfb5e436ad598ed17ad up to, but not including, e25447c35f8745337ea8bc0c9697fcac14df8605; af7cf057933f01dc7f33ddfb5e436ad598ed17ad up to, but not including, 1daf52b5ffb24870fbeda20b4967526d8f9e12ab; af7cf057933f01dc7f33ddfb5e436ad598ed17ad up to, but not including, cf54f66e1dd78990ec6b32177bca7e6ea2144a95; af7cf057933f01dc7f33ddfb5e436ad598ed17ad up to, but not including, 17f46b803d4f23c66cacce81db35fef3adb8f2af; and 1 more ranges | 6cd3f13aaa62970b5169d990e936b2e96943bc6a, 4595d90b5d2ea5fa4d318d13f59055aa4bf3e7f5, 80d24b308b7ee7037fc90d8ac99f6f78df0a256f, 3abc2d160ed8213948b147295d77d44a22c88fa3, e25447c35f8745337ea8bc0c9697fcac14df8605, 1daf52b5ffb24870fbeda20b4967526d8f9e12ab |
| Siemens | SIMATIC S7-1500 TM MFP - GNU/Linux subsystem | before V1.1.1 | V1.1.1 |
| Linux | Linux Kernel | before 5.10.215; 5.11 up to, but not including, 5.15.154; 5.16 up to, but not including, 6.1.84; 6.2 up to, but not including, 6.6.24; 6.7 up to, but not including, 6.7.12; 6.8 up to, but not including, 6.8.3 | 5.10.215, 5.15.154, 6.1.84, 6.6.24, 6.7.12, 6.8.3 |
| Debian | Debian Linux | 10.0 | Not stated |
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 | CNA |
| CVSS 3.1 | 7.8 | High | NVD |
Official description
In the Linux kernel, the following vulnerability has been resolved: nfs: fix UAF in direct writes In production we have been hitting the following warning consistently ------------[ cut here ]------------ refcount_t: underflow; use-after-free. WARNING: CPU: 17 PID: 1800359 at lib/refcount.c:28 refcount_warn_saturate+0x9c/0xe0 Workqueue: nfsiod nfs_direct_write_schedule_work [nfs] RIP: 0010:refcount_warn_saturate+0x9c/0xe0 PKRU: 55555554 Call Trace: <TASK> ? __warn+0x9f/0x130 ? refcount_warn_saturate+0x9c/0xe0 ? report_bug+0xcc/0x150 ? handle_bug+0x3d/0x70 ? exc_invalid_op+0x16/0x40 ? asm_exc_invalid_op+0x16/0x20 ? refcount_warn_saturate+0x9c/0xe0 nfs_direct_write_schedule_work+0x237/0x250 [nfs] process_one_work+0x12f/0x4a0 worker_thread+0x14e/0x3b0 ? ZSTD_getCParams_internal+0x220/0x220 kthread+0xdc/0x120 ? __btf_name_valid+0xa0/0xa0 ret_from_fork+0x1f/0x30 This is because we're completing the nfs_direct_request twice in a row. The source of this is when we have our commit requests to submit, we process them and send them off, and then in the completion path for the commit requests we have if (nfs_commit_end(cinfo.mds)) nfs_direct_write_complete(dreq); However since we're submitting asynchronous requests we sometimes have one that completes before we submit the next one, so we end up calling complete on the nfs_direct_request twice. The only other place we use nfs_generic_commit_list() is in __nfs_commit_inode, which wraps this call in a nfs_commit_begin(); nfs_commit_end(); Which is a common pattern for this style of completion handling, one that is also repeated in the direct code with get_dreq()/put_dreq() calls around where we process events as well as in the completion paths. Fix this by using the same pattern for the commit requests. Before with my 200 node rocksdb stress running this warning would pop every 10ish minutes. With my patch the stress test has been running for several hours without popping.
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/17f46b803d4f23c66cacce81db35fef3adb8f2af
- git.kernel.org/stable/c/1daf52b5ffb24870fbeda20b4967526d8f9e12ab
- git.kernel.org/stable/c/3abc2d160ed8213948b147295d77d44a22c88fa3
- git.kernel.org/stable/c/4595d90b5d2ea5fa4d318d13f59055aa4bf3e7f5
- git.kernel.org/stable/c/80d24b308b7ee7037fc90d8ac99f6f78df0a256f
- git.kernel.org/stable/c/cf54f66e1dd78990ec6b32177bca7e6ea2144a95
- git.kernel.org/stable/c/e25447c35f8745337ea8bc0c9697fcac14df8605
Third-party and government advisories
- lists.debian.org/debian-lts-announce/2024/06/msg00017.htmlMailing List, Third Party Advisory
Other references
Recent Use After Free vulnerabilities
- 9.8 Critical severity
- 8.8 High severity
- 8.8 High severity
- 7.8 High severity
- 7.8 High severity
- 7.8 High severity
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