Linux: Concurrent Execution using Shared Resource with Improper Synchronization
CVE-2026-31700 is a high-severity concurrent execution using shared resource with improper synchronization 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 0f4c9754956b86de158a4af5278c5cf5bda9439e, 714aa973da8163925eda7efd49361ccbee21ee46, 1490f82353bdabc09265a74e645b07f05cf4188e 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 0.11% 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 0f4c9754956b86de158a4af5278c5cf5bda9439e or 714aa973da8163925eda7efd49361ccbee21ee46 or 1490f82353bdabc09265a74e645b07f05cf4188e or 74e2db36fe50e3ad9d5300d7fd0e6e2a15a6d121, whichever matches your release line, or a later version.
- Update Linux Kernel to 6.6.136 or 6.12.84 or 6.18.25 or 7.0.2, whichever matches your release line, or a later version.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Linux | Linux | 1d036d25e5609ba73fee6a88db01c306b140d512 up to, but not including, 0f4c9754956b86de158a4af5278c5cf5bda9439e; 1d036d25e5609ba73fee6a88db01c306b140d512 up to, but not including, 714aa973da8163925eda7efd49361ccbee21ee46; 1d036d25e5609ba73fee6a88db01c306b140d512 up to, but not including, 1490f82353bdabc09265a74e645b07f05cf4188e; 1d036d25e5609ba73fee6a88db01c306b140d512 up to, but not including, 74e2db36fe50e3ad9d5300d7fd0e6e2a15a6d121; 1d036d25e5609ba73fee6a88db01c306b140d512 up to, but not including, 3a1bf9116ea31470b89692585c3910dfe830dcdd; 1d036d25e5609ba73fee6a88db01c306b140d512 up to, but not including, 28324a3b62d9ce7f9bdd65a8ce63f382041d1b27; 1d036d25e5609ba73fee6a88db01c306b140d512 up to, but not including, 48a6ef291a17639e1b6ae0fbe9c8b2bb87d7804b; 1d036d25e5609ba73fee6a88db01c306b140d512 up to, but not including, 2c054e17d9d41f1020376806c7f750834ced4dc5; and 1 more ranges | 0f4c9754956b86de158a4af5278c5cf5bda9439e, 714aa973da8163925eda7efd49361ccbee21ee46, 1490f82353bdabc09265a74e645b07f05cf4188e, 74e2db36fe50e3ad9d5300d7fd0e6e2a15a6d121, 3a1bf9116ea31470b89692585c3910dfe830dcdd, 28324a3b62d9ce7f9bdd65a8ce63f382041d1b27 |
| 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 | 4.6 up to, but not including, 6.6.136; 6.7 up to, but not including, 6.12.84; 6.13 up to, but not including, 6.18.25; 6.19 up to, but not including, 7.0.2; 7.1 | 6.6.136, 6.12.84, 6.18.25, 7.0.2 |
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.
Official description
In the Linux kernel, the following vulnerability has been resolved: net/packet: fix TOCTOU race on mmap'd vnet_hdr in tpacket_snd() In tpacket_snd(), when PACKET_VNET_HDR is enabled, vnet_hdr points directly into the mmap'd TX ring buffer shared with userspace. The kernel validates the header via __packet_snd_vnet_parse() but then re-reads all fields later in virtio_net_hdr_to_skb(). A concurrent userspace thread can modify the vnet_hdr fields between validation and use, bypassing all safety checks. The non-TPACKET path (packet_snd()) already correctly copies vnet_hdr to a stack-local variable. All other vnet_hdr consumers in the kernel (tun.c, tap.c, virtio_net.c) also use stack copies. The TPACKET TX path is the only caller of virtio_net_hdr_to_skb() that reads directly from user-controlled shared memory. Fix this by copying vnet_hdr from the mmap'd ring buffer to a stack-local variable before validation and use, consistent with the approach used in packet_snd() and all other callers.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Concurrent Execution using Shared Resource with Improper Synchronization
The product contains a concurrent code sequence that requires temporary, exclusive access to a shared resource, but a timing window exists in which the shared resource can be modified by another code sequence operating concurrently.
How developers prevent this class of flaw
- In languages that support it, use synchronization primitives. Only wrap these around critical code to minimize the impact on performance.
- Use thread-safe capabilities such as the data access abstraction in Spring.
- Minimize the usage of shared resources in order to remove as much complexity as possible from the control flow and to reduce the likelihood of unexpected conditions occurring. Additionally, this will minimize the amount of synchronization necessary and may even help to reduce the likelihood of a denial of service where an attacker may be able to repeatedly trigger a critical section (CWE-400).
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/28324a3b62d9ce7f9bdd65a8ce63f382041d1b27
- git.kernel.org/stable/c/2c054e17d9d41f1020376806c7f750834ced4dc5
- git.kernel.org/stable/c/3a1bf9116ea31470b89692585c3910dfe830dcdd
- git.kernel.org/stable/c/48a6ef291a17639e1b6ae0fbe9c8b2bb87d7804b
- git.kernel.org/stable/c/74e2db36fe50e3ad9d5300d7fd0e6e2a15a6d121
Other references
- git.kernel.org/stable/c/0f4c9754956b86de158a4af5278c5cf5bda9439e
- git.kernel.org/stable/c/1490f82353bdabc09265a74e645b07f05cf4188e
- git.kernel.org/stable/c/714aa973da8163925eda7efd49361ccbee21ee46
- cert-portal.siemens.com/productcert/html/ssa-019113.html
- cert-portal.siemens.com/productcert/html/ssa-457936.html
- cert-portal.siemens.com/productcert/html/ssa-784472.html
Recent Concurrent Execution using Shared Resource with Improper Synchronization vulnerabilities
- 7.8 High severity
- 7.8 High severity
- 7.0 High severity
- 7.5 High severity
- 7.8 High severity
- 7.8 High severity
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