bcrypt-ruby is a Ruby binding for the OpenBSD bcrypt() password hashing algorithm. Prior to version 3.1.22, an integer overflow in the Java BCrypt implementation for JRuby can cause zero iterations in the strengthening loop. Impacted applications must be setting the cost to 31 to see this happen. The JRuby implementation of bcrypt-ruby (`BCrypt.java`) computes the key-strengthening round count as a signed 32-bit integer. When `cost=31` (the maximum allowed by the gem), signed integer overflow causes the round count to become negative, and the strengthening loop executes **zero iterations**. This collapses bcrypt from 2^31 rounds of exponential key-strengthening to effectively constant-time computation — only the initial EksBlowfish key setup and final 64x encryption phase remain. The resulting hash looks valid (`$2a$31$...`) and verifies correctly via `checkpw`, making the weakness invisible to the application. This issue is triggered only when cost=31 is used or when verifying a `$2a$31$` hash. This problem has been fixed in version 3.1.22. As a workaround, set the cost to something less than 31.

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

  - bcrypt-ruby is a Ruby binding for the OpenBSD bcrypt() password hashing algorithm. Prior to version
    3.1.22, an integer overflow in the Java BCrypt implementation for JRuby can cause zero iterations in the
    strengthening loop. Impacted applications must be setting the cost to 31 to see this happen. The JRuby
    implementation of bcrypt-ruby (`BCrypt.java`) computes the key-strengthening round count as a signed
    32-bit integer. When `cost=31` (the maximum allowed by the gem), signed integer overflow causes the round
    count to become negative, and the strengthening loop executes **zero iterations**. This collapses bcrypt
    from 2^31 rounds of exponential key-strengthening to effectively constant-time computation — only the
    initial EksBlowfish key setup and final 64x encryption phase remain. The resulting hash looks valid
    (`$2a$31$...`) and verifies correctly via `checkpw`, making the weakness invisible to the application.
    This issue is triggered only when cost=31 is used or when verifying a `$2a$31$` hash. This problem has
    been fixed in version 3.1.22. As a workaround, set the cost to something less than 31. (CVE-2026-33306)

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

  - bcrypt-ruby is a Ruby binding for the OpenBSD bcrypt() password hashing algorithm. Prior to version     3.1.22, an integer overflow in the Java BCrypt implementation for JRuby can cause zero iterations in the     strengthening loop. Impacted applications must be setting the cost to 31 to see this happen. The JRuby     implementation of bcrypt-ruby (`BCrypt.java`) computes the key-strengthening round count as a signed     32-bit integer. When `cost=31` (the maximum allowed by the gem), signed integer overflow causes the round     count to become negative, and the strengthening loop executes **zero iterations**. This collapses bcrypt     from 2^31 rounds of exponential key-strengthening to effectively constant-time computation  only the     initial EksBlowfish key setup and final 64x encryption phase remain. The resulting hash looks valid     (`$2a$31$...`) and verifies correctly via `checkpw`, making the weakness invisible to the application.
    This issue is triggered only when cost=31 is used or when verifying a `$2a$31$` hash. This problem has     been fixed in version 3.1.22. As a workaround, set the cost to something less than 31. (CVE-2026-33306)

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

ID	Name	Product	Family	Severity
439244	SCA: security update for bcrypt (GHSA-f27w-vcwj-c954)	Tenable Cloud Security	SCA Checks	high
439244	SCA: security update for bcrypt (GHSA-f27w-vcwj-c954)	Tenable Self-Hosted Container Security	SCA Checks	high
303306	Linux Distros Unpatched Vulnerability : CVE-2026-33306	Nessus	Misc.	high

Detections

Analytics

CVE-2026-33306

high

Tenable Plugins

high

high

high