Linux Kernel up to 6.18.7/6.19-rc6 fpsimd task_fpsimd_load allocation of resources

Summaryinfo

A vulnerability classified as critical was found in Linux Kernel up to 6.18.7/6.19-rc6. Affected by this vulnerability is the function task_fpsimd_load of the component fpsimd. Executing a manipulation can lead to allocation of resources. The identification of this vulnerability is CVE-2026-23102. There is no exploit available. Upgrading the affected component is advised.

Detailsinfo

A vulnerability has been found in Linux Kernel up to 6.18.7/6.19-rc6 and classified as critical. This vulnerability affects the function task_fpsimd_load of the component fpsimd. The manipulation with an unknown input leads to a allocation of resources vulnerability. The CWE definition for the vulnerability is CWE-770. The product allocates a reusable resource or group of resources on behalf of an actor without imposing any restrictions on the size or number of resources that can be allocated, in violation of the intended security policy for that actor. The impact remains unknown. CVE summarizes:

In the Linux kernel, the following vulnerability has been resolved: arm64/fpsimd: signal: Fix restoration of SVE context When SME is supported, Restoring SVE signal context can go wrong in a few ways, including placing the task into an invalid state where the kernel may read from out-of-bounds memory (and may potentially take a fatal fault) and/or may kill the task with a SIGKILL. (1) Restoring a context with SVE_SIG_FLAG_SM set can place the task into an invalid state where SVCR.SM is set (and sve_state is non-NULL) but TIF_SME is clear, consequently resuting in out-of-bounds memory reads and/or killing the task with SIGKILL. This can only occur in unusual (but legitimate) cases where the SVE signal context has either been modified by userspace or was saved in the context of another task (e.g. as with CRIU), as otherwise the presence of an SVE signal context with SVE_SIG_FLAG_SM implies that TIF_SME is already set. While in this state, task_fpsimd_load() will NOT configure SMCR_ELx (leaving some arbitrary value configured in hardware) before restoring SVCR and attempting to restore the streaming mode SVE registers from memory via sve_load_state(). As the value of SMCR_ELx.LEN may be larger than the task's streaming SVE vector length, this may read memory outside of the task's allocated sve_state, reading unrelated data and/or triggering a fault. While this can result in secrets being loaded into streaming SVE registers, these values are never exposed. As TIF_SME is clear, fpsimd_bind_task_to_cpu() will configure CPACR_ELx.SMEN to trap EL0 accesses to streaming mode SVE registers, so these cannot be accessed directly at EL0. As fpsimd_save_user_state() verifies the live vector length before saving (S)SVE state to memory, no secret values can be saved back to memory (and hence cannot be observed via ptrace, signals, etc). When the live vector length doesn't match the expected vector length for the task, fpsimd_save_user_state() will send a fatal SIGKILL signal to the task. Hence the task may be killed after executing userspace for some period of time. (2) Restoring a context with SVE_SIG_FLAG_SM clear does not clear the task's SVCR.SM. If SVCR.SM was set prior to restoring the context, then the task will be left in streaming mode unexpectedly, and some register state will be combined inconsistently, though the task will be left in legitimate state from the kernel's PoV. This can only occur in unusual (but legitimate) cases where ptrace has been used to set SVCR.SM after entry to the sigreturn syscall, as syscall entry clears SVCR.SM. In these cases, the the provided SVE register data will be loaded into the task's sve_state using the non-streaming SVE vector length and the FPSIMD registers will be merged into this using the streaming SVE vector length. Fix (1) by setting TIF_SME when setting SVCR.SM. This also requires ensuring that the task's sme_state has been allocated, but as this could contain live ZA state, it should not be zeroed. Fix (2) by clearing SVCR.SM when restoring a SVE signal context with SVE_SIG_FLAG_SM clear. For consistency, I've pulled the manipulation of SVCR, TIF_SVE, TIF_SME, and fp_type earlier, immediately after the allocation of sve_state/sme_state, before the restore of the actual register state. This makes it easier to ensure that these are always modified consistently, even if a fault is taken while reading the register data from the signal context. I do not expect any software to depend on the exact state restored when a fault is taken while reading the context.

The advisory is shared for download at git.kernel.org. This vulnerability was named CVE-2026-23102 since 01/13/2026. The exploitation appears to be difficult. There are known technical details, but no exploit is available.

The vulnerability scanner Nessus provides a plugin with the ID 297969 (Linux Distros Unpatched Vulnerability : CVE-2026-23102), which helps to determine the existence of the flaw in a target environment.

Upgrading to version 6.18.8 or 6.19-rc7 eliminates this vulnerability. Applying the patch 7b5a52cf252a0d2e89787b645290ad288878f332/d2907cbe9ea0a54cbe078076f9d089240ee1e2d9 is able to eliminate this problem. The bugfix is ready for download at git.kernel.org. The best possible mitigation is suggested to be upgrading to the latest version.

The vulnerability is also documented in the databases at Tenable (297969) and CERT Bund (WID-SEC-2026-0324). VulDB is the best source for vulnerability data and more expert information about this specific topic.

Affected

• Debian Linux
• Google Cloud Platform
• Amazon Linux 2
• Red Hat Enterprise Linux
• Ubuntu Linux
• SUSE Linux
• Oracle Linux
• IBM QRadar SIEM
• SUSE openSUSE
• RESF Rocky Linux
• Open Source Linux Kernel

Productinfo

Type

• Operating System

Vendor

• Linux

Name

• Kernel

Version

• 6.18.0
• 6.18.1
• 6.18.2
• 6.18.3
• 6.18.4
• 6.18.5
• 6.18.6
• 6.18.7
• 6.19-rc1
• 6.19-rc2
• 6.19-rc3
• 6.19-rc4
• 6.19-rc5
• 6.19-rc6

License

• open-source

Website

• Vendor: https://www.kernel.org/

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Entryinfo

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