CVE-2025-21909

In the Linux kernel, the following vulnerability has been resolved:

wifi: nl80211: reject cooked mode if it is set along with other flags

It is possible to set both MONITOR_FLAG_COOK_FRAMES and MONITOR_FLAG_ACTIVE flags simultaneously on the same monitor interface from the userspace. This causes a sub-interface to be created with no IEEE80211_SDATA_IN_DRIVER bit set because the monitor interface is in the cooked state and it takes precedence over all other states. When the interface is then being deleted the kernel calls WARN_ONCE() from check_sdata_in_driver() because of missing that bit.

Fix this by rejecting MONITOR_FLAG_COOK_FRAMES if it is set along with other flags.

Found by Linux Verification Center (linuxtesting.org) with Syzkaller.

Weakness

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.

Affected Software

Extended Description

A race condition occurs within concurrent environments, and it is effectively a property of a code sequence. Depending on the context, a code sequence may be in the form of a function call, a small number of instructions, a series of program invocations, etc. A race condition violates these properties, which are closely related:

A race condition exists when an “interfering code sequence” can still access the shared resource, violating exclusivity. The interfering code sequence could be “trusted” or “untrusted.” A trusted interfering code sequence occurs within the product; it cannot be modified by the attacker, and it can only be invoked indirectly. An untrusted interfering code sequence can be authored directly by the attacker, and typically it is external to the vulnerable product.

Potential Mitigations

• 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).

Related Attack Patterns

• https://cwe.mitre.org/data/definitions/26.html
• https://cwe.mitre.org/data/definitions/29.html

References

• https://git.kernel.org/stable/c/236f41ca728f23210b31ed2d1d8a6df575a4b2d6
• https://git.kernel.org/stable/c/351eb7ac53ff1cd94d893c0c4534ced2f36ae7d7
• https://git.kernel.org/stable/c/49f27f29446a5bfe633dd2cc0cfebd48a1a5e77f
• https://git.kernel.org/stable/c/521e55c2b0d6028861ac0a2d06aa57bb0e3ac486
• https://git.kernel.org/stable/c/5ea856d93794c4afa5542defd8c61f2708dc245a
• https://git.kernel.org/stable/c/ac4860141300581d3e2f6c6dafa37220f7ea9f65
• https://git.kernel.org/stable/c/cd1bdcb77fdc03c253137e55bae10551b3481461
• https://git.kernel.org/stable/c/ebebbb0eded2ed9a1abfa31962f6fb699e6abce7
• https://lists.debian.org/debian-lts-announce/2025/05/msg00030.html
• https://lists.debian.org/debian-lts-announce/2025/05/msg00045.html