Linux: Use After Free
CVE-2024-56631 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 e19acb1926c4a1f30ee1ec84d8afba2d975bd534, 285ce1f89f8d414e7eecab5ef5118cd512596318, 198b89dd5a595ee3f96e5ce5c448b0484cd0e53c 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 0.29% 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 e19acb1926c4a1f30ee1ec84d8afba2d975bd534 or 285ce1f89f8d414e7eecab5ef5118cd512596318 or 198b89dd5a595ee3f96e5ce5c448b0484cd0e53c or 275b8347e21ab8193e93223a8394a806e4ba8918, 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 6.6.66 or 6.12.5, whichever matches your release line, or a later version.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Linux | Linux | cc833acbee9db5ca8c6162b015b4c93863c6f821 up to, but not including, e19acb1926c4a1f30ee1ec84d8afba2d975bd534; cc833acbee9db5ca8c6162b015b4c93863c6f821 up to, but not including, 285ce1f89f8d414e7eecab5ef5118cd512596318; cc833acbee9db5ca8c6162b015b4c93863c6f821 up to, but not including, 198b89dd5a595ee3f96e5ce5c448b0484cd0e53c; cc833acbee9db5ca8c6162b015b4c93863c6f821 up to, but not including, 275b8347e21ab8193e93223a8394a806e4ba8918; cc833acbee9db5ca8c6162b015b4c93863c6f821 up to, but not including, 59b30afa578637169e2819536bb66459fdddc39d; cc833acbee9db5ca8c6162b015b4c93863c6f821 up to, but not including, 1f5e2f1ca5875728fcf62bc1a054707444ab4960; cc833acbee9db5ca8c6162b015b4c93863c6f821 up to, but not including, f10593ad9bc36921f623361c9e3dd96bd52d85ee; 3a27c0defb0315760100f8b1adc7c4acbe04c884; and 2 more ranges | e19acb1926c4a1f30ee1ec84d8afba2d975bd534, 285ce1f89f8d414e7eecab5ef5118cd512596318, 198b89dd5a595ee3f96e5ce5c448b0484cd0e53c, 275b8347e21ab8193e93223a8394a806e4ba8918, 59b30afa578637169e2819536bb66459fdddc39d, 1f5e2f1ca5875728fcf62bc1a054707444ab4960 |
| Siemens | SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AB0) | V3.1.6 and later; V3.1.7 and later | Not stated |
| Siemens | SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AC0) | V3.1.6 and later; V3.1.7 and later | Not stated |
| Siemens | SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AB0) | V3.1.6 and later; V3.1.7 and later | Not stated |
| Siemens | SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AC0) | V3.1.6 and later; V3.1.7 and later | Not stated |
| Siemens | SIMATIC S7-1500 TM MFP - GNU/Linux subsystem | before V1.1.1 | V1.1.1 |
| Siemens | SIPLUS S7-1500 CPU 1518-4 PN/DP MFP (6AG1518-4AX00-4AC0) | V3.1.6 and later; V3.1.7 and later | Not stated |
| Linux | Linux Kernel | 3.16.85 up to, but not including, 6.6.66; 6.7 up to, but not including, 6.12.5; 6.13 | 6.6.66, 6.12.5 |
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 |
| CVSS 3.1 | 7.8 | High | CISA (ADP) |
Official description
In the Linux kernel, the following vulnerability has been resolved: scsi: sg: Fix slab-use-after-free read in sg_release() Fix a use-after-free bug in sg_release(), detected by syzbot with KASAN: BUG: KASAN: slab-use-after-free in lock_release+0x151/0xa30 kernel/locking/lockdep.c:5838 __mutex_unlock_slowpath+0xe2/0x750 kernel/locking/mutex.c:912 sg_release+0x1f4/0x2e0 drivers/scsi/sg.c:407 In sg_release(), the function kref_put(&sfp->f_ref, sg_remove_sfp) is called before releasing the open_rel_lock mutex. The kref_put() call may decrement the reference count of sfp to zero, triggering its cleanup through sg_remove_sfp(). This cleanup includes scheduling deferred work via sg_remove_sfp_usercontext(), which ultimately frees sfp. After kref_put(), sg_release() continues to unlock open_rel_lock and may reference sfp or sdp. If sfp has already been freed, this results in a slab-use-after-free error. Move the kref_put(&sfp->f_ref, sg_remove_sfp) call after unlocking the open_rel_lock mutex. This ensures: - No references to sfp or sdp occur after the reference count is decremented. - Cleanup functions such as sg_remove_sfp() and sg_remove_sfp_usercontext() can safely execute without impacting the mutex handling in sg_release(). The fix has been tested and validated by syzbot. This patch closes the bug reported at the following syzkaller link and ensures proper sequencing of resource cleanup and mutex operations, eliminating the risk of use-after-free errors in sg_release().
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
Other references
- git.kernel.org/stable/c/198b89dd5a595ee3f96e5ce5c448b0484cd0e53c
- git.kernel.org/stable/c/275b8347e21ab8193e93223a8394a806e4ba8918
- git.kernel.org/stable/c/285ce1f89f8d414e7eecab5ef5118cd512596318
- git.kernel.org/stable/c/e19acb1926c4a1f30ee1ec84d8afba2d975bd534
- lists.debian.org/debian-lts-announce/2025/03/msg00001.html
- lists.debian.org/debian-lts-announce/2025/03/msg00002.html
- cert-portal.siemens.com/productcert/html/ssa-019113.html
- cert-portal.siemens.com/productcert/html/ssa-265688.html
- cert-portal.siemens.com/productcert/html/ssa-457936.html
Recent Use After Free vulnerabilities
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- 7.0 High severity
- 7.8 High severity
- 7.8 High severity
- 7.8 High severity
- 7.8 High severity
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