Integer Overflow or Wraparound Affecting ruby-bcrypt package, versions <3.1.22-1


Severity

Recommended
0.0
high
0
10

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Threat Intelligence

EPSS
0.24% (15th percentile)

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  • Snyk IDSNYK-DEBIANUNSTABLE-RUBYBCRYPT-15764372
  • published26 Mar 2026
  • disclosed24 Mar 2026

Introduced: 24 Mar 2026

CVE-2026-33306  (opens in a new tab)
CWE-190  (opens in a new tab)

How to fix?

Upgrade Debian:unstable ruby-bcrypt to version 3.1.22-1 or higher.

NVD Description

Note: Versions mentioned in the description apply only to the upstream ruby-bcrypt package and not the ruby-bcrypt package as distributed by Debian. See How to fix? for Debian:unstable relevant fixed versions and status.

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.

CVSS Base Scores

version 3.1