CVE-2026-54905: ruby-concurrency concurrent-ruby Wrap-around Error

Vulnerability summary

CVE-2026-54905 is a medium (CVSS 5.5) Wrap-around Error vulnerability in ruby-concurrency concurrent-ruby. EPSS estimates a 0.15% chance of exploitation in the next 30 days, higher than 4% of scored vulnerabilities.

Timeline

1. 24-06-2026
   PublishedVulnerability first disclosed.
2. 24-06-2026
   Last modifiedVulnerability information updated.

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.

• CWE-128Wrap-around ErrorWrap around errors occur whenever a value is incremented past the maximum value for its type and therefore "wraps around" to a very small, negative, or undefined value.