UBUNTU-CVE-2026-33306

See a problem?
Please try reporting it to the source first.

Source

https://ubuntu.com/security/CVE-2026-33306

Import Source

https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-33306.json

JSON Data

https://api.osv.dev/v1/vulns/UBUNTU-CVE-2026-33306

Upstream

CVE-2026-33306

Published

2026-03-24T01:17:00Z

Modified

2026-04-02T21:20:48.429851Z

Severity

4.5 (Medium) CVSS_V4 - CVSS:4.0/AV:L/AC:H/AT:P/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N/E:U CVSS Calculator
7.5 (High) CVSS_V3 - CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N CVSS Calculator
Ubuntu - medium

Summary

[none]

Details

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.

References

Affected packages

Ubuntu:16.04:LTS / bcrypt

Package

Name: bcrypt
Purl: pkg:deb/ubuntu/bcrypt@1.1-8.1?arch=source&distro=xenial

Affected ranges

Type: ECOSYSTEM
Events: Introduced

0Unknown introduced version / All previous versions are affected

Affected versions

1.*

1.1-8.1

Ecosystem specific

{
    "binaries": [
        {
            "binary_name": "bcrypt",
            "binary_version": "1.1-8.1"
        }
    ]
}

Database specific

source

"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-33306.json"

Ubuntu:18.04:LTS / bcrypt