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Medium severity5.5NVD Advisory· Published Jun 24, 2026· Updated Jun 26, 2026

CVE-2026-54905

CVE-2026-54905

Description

concurrent-ruby is a modern concurrency tools for Ruby. Prior to 1.3.7, Concurrent::ReentrantReadWriteLock can incorrectly grant a write lock after one thread acquires the read lock 32,768 times. The lock stores a thread's local read and write hold counts in one integer. The low 15 bits are used for the read hold count, and bit 15 is used as WRITE_LOCK_HELD. After 32,768 reentrant read acquisitions, the local read count crosses into the write-lock bit. try_write_lock then treats the thread as already holding a write lock and returns true without setting the global RUNNING_WRITER bit. This breaks the core mutual-exclusion guarantee: the caller is told it has a write lock, but other threads can still hold or acquire read locks at the same time. This vulnerability is fixed in 1.3.7.

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Affected packages

Versions sourced from the GitHub Security Advisory.

PackageAffected versionsPatched versions
concurrent-rubyRubyGems
< 1.3.71.3.7

Affected products

57

Patches

Vulnerability mechanics

References

5

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