concurrent-ruby is a modern concurrency tools for Ruby. Prior to 1.3.7, Concurrent::ReadWriteLock#release_write_lock does not verify that the calling thread acquired the write lock. Any thread with access to the lock object can release an active write lock held by another thread. A second writer can then enter its critical section while the first writer is still running. Concurrent::ReadWriteLock#release_read_lock also decrements the shared counter even when no read lock is held. Calling it on a fresh lock changes the counter from 0 to -1, after which normal read acquisition raises Concurrent::ResourceLimitError. This is a synchronization correctness issue in the public Concurrent::ReadWriteLock API. This vulnerability is fixed in 1.3.7.

photon_os PHSA-2026-5.0-91-0909: Unknown PhotonOS Security Updated

An update of the rubygem package has been released.

The Linux/Unix host has one or more packages installed that are impacted by a vulnerability without a vendor supplied patch available.

  - concurrent-ruby is a modern concurrency tools for Ruby. Prior to 1.3.7,     Concurrent::ReadWriteLock#release_write_lock does not verify that the calling thread acquired the write     lock. Any thread with access to the lock object can release an active write lock held by another thread. A     second writer can then enter its critical section while the first writer is still running.
    Concurrent::ReadWriteLock#release_read_lock also decrements the shared counter even when no read lock is     held. Calling it on a fresh lock changes the counter from 0 to -1, after which normal read acquisition     raises Concurrent::ResourceLimitError. This is a synchronization correctness issue in the public     Concurrent::ReadWriteLock API. This vulnerability is fixed in 1.3.7. (CVE-2026-54906)

Note that Nessus relies on the presence of the package as reported by the vendor.

There are packages installed that are affected by a vulnerability referenced in the following CVE:

  - concurrent-ruby is a modern concurrency tools for Ruby. Prior to 1.3.7,
    Concurrent::ReadWriteLock#release_write_lock does not verify that the calling thread acquired the write
    lock. Any thread with access to the lock object can release an active write lock held by another thread. A
    second writer can then enter its critical section while the first writer is still running.
    Concurrent::ReadWriteLock#release_read_lock also decrements the shared counter even when no read lock is
    held. Calling it on a fresh lock changes the counter from 0 to -1, after which normal read acquisition
    raises Concurrent::ResourceLimitError. This is a synchronization correctness issue in the public
    Concurrent::ReadWriteLock API. This vulnerability is fixed in 1.3.7. (CVE-2026-54906)

ID	Name	Product	Family	Severity
332674	Photon OS 5.0: Rubygem PHSA-2026-5.0-90-0929	Nessus	PhotonOS Local Security Checks	high
329736	Photon OS 5.0: Rubygem PHSA-2026-5.0-0929	Nessus	PhotonOS Local Security Checks	high
325966	Photon OS 4.0: Rubygem PHSA-2026-4.0-1046	Nessus	PhotonOS Local Security Checks	low
323931	Photon OS 5.0: Rubygem PHSA-2026-5.0-0909	Nessus	PhotonOS Local Security Checks	high
322704	Linux Distros Unpatched Vulnerability : CVE-2026-54906	Nessus	Misc.	low
443732	SCA: security update for concurrent-ruby (GHSA-6wx8-w4f5-wwcr)	Tenable Cloud Security	SCA Checks	low
443732	SCA: security update for concurrent-ruby (GHSA-6wx8-w4f5-wwcr)	Tenable Self-Hosted Container Security	SCA Checks	low

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CVE-2026-54906

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