Reference page — cumulative record through Wednesday, August 19, 2026 UTC. Reference pages update as the archive grows; only dated daily editions are immutable pages of record.
AV AC PR UI S C I A CVSS EPSS %ile KEV L L L N U H N N 5.5 .0024 14.8 —
AFFECTED Product Versions Fixed Linux b519b56e378ee82caf9b079b04f5db87dedc3251 – — Linux 4.15 – 4.19.189
TIMELINE Feb 25 Reserved by Linux Feb 27 Published (CNA: Linux) Aug 4 RESCORED — CVE-2021-46921 (Linux). CVSS 7.8 → 5.5 (NVD).
In the Linux kernel, the following vulnerability has been resolved: locking/qrwlock: Fix ordering in queued_write_lock_slowpath() While this code is executed with the wait_lock held, a reader can acquire the lock without holding wait_lock. The writer side loops checking the value with the atomic_cond_read_acquire(), but only truly acquires the lock when the compare-and-exchange is completed successfully which isn’t ordered. This exposes the window between the acquire and the cmpxchg to an A-B-A problem which allows reads following the lock acquisition to observe values speculatively before the write lock is truly acquired. We've seen a problem in epoll where the reader does a xchg while holding the read lock, but the writer can see a value change out from under it. Writer | Reader -------------------------------------------------------------------------------- ep_scan_ready_list() | |- write_lock_irq() | |- queued_write_lock_slowpath() | |- atomic_cond_read_acquire() | | read_lock_irqsave(&ep->lock, flags); --> (observes value before unlock) | chain_epi_lockless() | | epi->next = xchg(&ep->ovflist, epi); | | read_unlock_irqrestore(&ep->lock, flags); | | | atomic_cmpxchg_relaxed() | |-- READ_ONCE(ep->ovflist); | A core can order the read of the ovflist ahead of the atomic_cmpxchg_relaxed(). Switching the cmpxchg to use acquire semantics addresses this issue at which point the atomic_cond_read can be switched to use relaxed semantics. [peterz: use try_cmpxchg()]
| Date | Event | Detail |
|---|---|---|
| February 25, 2024 | Reserved | Reserved by Linux |
| February 27, 2024 | Published | Published (CNA: Linux) |
| August 4, 2026 | RESCORED | RESCORED — CVE-2021-46921 (Linux). CVSS 7.8 → 5.5 (NVD). |
Authoritative record: CVE-2021-46921 at cve.org
Vendors: linux
Weaknesses: CWE-668
This is a reference page, not a dated page of record. It assembles the complete lifecycle of CVE-2021-46921 from the CVE Program record, NVD enrichment, the CISA KEV catalog, EPSS, and OSV advisories. The box score's numbers (CVSS, EPSS, KEV status) are current as of Wednesday, August 19, 2026 UTC and are re-derived as the archive grows; only dated daily editions are immutable pages of record. The authoritative source for this identifier is cve.org.