Linux: Use After Free
CVE-2026-52943 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 8dbed691e43a50903658130bde0fcb5abc425b37, 9b40bdc2a3298225dffab8158208a0d8c6300578, fd470f0a97b8e9a125f520265d2f3b088ffb5b8a 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 0.3% 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 8dbed691e43a50903658130bde0fcb5abc425b37 or 9b40bdc2a3298225dffab8158208a0d8c6300578 or fd470f0a97b8e9a125f520265d2f3b088ffb5b8a or ceafb893b12f23331dcc5ff9587e643c3a40ee9f, 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.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Linux | Linux | 6fa01ccd883021105e9f8af7d04b9f156fa3494a up to, but not including, 8dbed691e43a50903658130bde0fcb5abc425b37; 6fa01ccd883021105e9f8af7d04b9f156fa3494a up to, but not including, 9b40bdc2a3298225dffab8158208a0d8c6300578; 6fa01ccd883021105e9f8af7d04b9f156fa3494a up to, but not including, fd470f0a97b8e9a125f520265d2f3b088ffb5b8a; 6fa01ccd883021105e9f8af7d04b9f156fa3494a up to, but not including, ceafb893b12f23331dcc5ff9587e643c3a40ee9f; 6fa01ccd883021105e9f8af7d04b9f156fa3494a up to, but not including, 2e0e74c59b2761a414d9f48d7bee1e45220b2427; 6fa01ccd883021105e9f8af7d04b9f156fa3494a up to, but not including, 96a4713ae041cc85e712bac682cd2e644004d6c6; 6fa01ccd883021105e9f8af7d04b9f156fa3494a up to, but not including, 474d6c771d798bca84f0a140b611e36743511e18; 6fa01ccd883021105e9f8af7d04b9f156fa3494a up to, but not including, 98d0912e9f841e5529a5b89a972805f34cb1c69d; and 1 more ranges | 8dbed691e43a50903658130bde0fcb5abc425b37, 9b40bdc2a3298225dffab8158208a0d8c6300578, fd470f0a97b8e9a125f520265d2f3b088ffb5b8a, ceafb893b12f23331dcc5ff9587e643c3a40ee9f, 2e0e74c59b2761a414d9f48d7bee1e45220b2427, 96a4713ae041cc85e712bac682cd2e644004d6c6 |
| Red Hat | Red Hat Enterprise Linux 10 | Not specified in the record | Not stated |
| Red Hat | Red Hat Enterprise Linux 6 | Not specified in the record | Not stated |
| Red Hat | Red Hat Enterprise Linux 7 | Not specified in the record | Not stated |
| Red Hat | Red Hat Enterprise Linux 8 | Not specified in the record | Not stated |
| Red Hat | Red Hat Enterprise Linux 9 | Not specified in the record | Not stated |
| 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 | all versions | Not stated |
| 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 | 4.7 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
- 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 | 7.8 | High | CNA |
Official description
In the Linux kernel, the following vulnerability has been resolved: net: skbuff: fix missing zerocopy reference in pskb_carve helpers pskb_carve_inside_header() and pskb_carve_inside_nonlinear() both copy the old skb_shared_info header into a new buffer via memcpy(), which includes the destructor_arg pointer (uarg) for MSG_ZEROCOPY skbs. Neither function calls net_zcopy_get() for the new shinfo, creating an unaccounted holder: every skb_shared_info with destructor_arg set will call skb_zcopy_clear() once when freed, but the corresponding net_zcopy_get() was never called for the new copy. Repeated calls drive uarg->refcnt to zero prematurely, freeing ubuf_info_msgzc while TX skbs still hold live destructor_arg pointers. KASAN reports use-after-free on a freed ubuf_info_msgzc: BUG: KASAN: slab-use-after-free in skb_release_data+0x77b/0x810 Read of size 8 at addr ffff88801574d3e8 by task poc/220 Call Trace: skb_release_data+0x77b/0x810 kfree_skb_list_reason+0x13e/0x610 skb_release_data+0x4cd/0x810 sk_skb_reason_drop+0xf3/0x340 skb_queue_purge_reason+0x282/0x440 rds_tcp_inc_free+0x1e/0x30 rds_recvmsg+0x354/0x1780 __sys_recvmsg+0xdf/0x180 Allocated by task 219: msg_zerocopy_realloc+0x157/0x7b0 tcp_sendmsg_locked+0x2892/0x3ba0 Freed by task 219: ip_recv_error+0x74a/0xb10 tcp_recvmsg+0x475/0x530 The skb consuming the late access still referenced the same uarg via shinfo->destructor_arg copied by pskb_carve_inside_nonlinear() without a refcount bump. This has been verified to be reliably exploitable: a working proof-of-concept achieves full root privilege escalation from an unprivileged local user on a default kernel configuration. The fix follows the pattern of pskb_expand_head() which has the same memcpy/cloned structure. For pskb_carve_inside_header(), net_zcopy_get() is placed after skb_orphan_frags() succeeds, so the orphan error path needs no cleanup. For pskb_carve_inside_nonlinear(), net_zcopy_get() is placed after all failure points and just before skb_release_data(), so no error path needs cleanup at all -- matching pskb_expand_head() more closely and avoiding the need for a balancing net_zcopy_put().
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/2e0e74c59b2761a414d9f48d7bee1e45220b2427
- git.kernel.org/stable/c/474d6c771d798bca84f0a140b611e36743511e18
- git.kernel.org/stable/c/8dbed691e43a50903658130bde0fcb5abc425b37
- git.kernel.org/stable/c/96a4713ae041cc85e712bac682cd2e644004d6c6
- git.kernel.org/stable/c/98d0912e9f841e5529a5b89a972805f34cb1c69d
- git.kernel.org/stable/c/9b40bdc2a3298225dffab8158208a0d8c6300578
- git.kernel.org/stable/c/ceafb893b12f23331dcc5ff9587e643c3a40ee9f
- git.kernel.org/stable/c/fd470f0a97b8e9a125f520265d2f3b088ffb5b8a
Third-party and government advisories
- access.redhat.com/security/cve/CVE-2026-52943Third Party Advisory
- bugzilla.redhat.com/show_bug.cgi?id=2492137Third Party Advisory
- security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-52943.jsonThird Party Advisory
Other references
Recent Use After Free vulnerabilities
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- 8.8 High severity
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- 9.6 Critical severity
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