Summary
Devise-Two-Factor Authentication Uses Insufficient Default OTP Shared Secret Length
Under the default configuration, Devise-Two-Factor versions 1.0.0 or >= 4.0.0 & < 6.0.0 generate TOTP shared secrets that are 120 bits instead of the 128-bit minimum defined by RFC 4226. Using a shared secret shorter than the minimum to generate a multi-factor authentication code could make it easier for an attacker to guess the shared secret and generate valid TOTP codes.
Background
Devise-Two-Factor uses ROTP to generate shared secrets for TOTP. In ROTP < 5.0.0, the first argument to the ROTP::Base32#random_base32 function represented the number of bytes to read from SecureRandom which were then returned as a base32-encoded string. In ROTP 5.1.0, this function was changed so that the first argument now represents the length of the base32-encoded string returned by the function instead of the number of bytes to read from SecureRandom resulting in a shorter key being generated for the same input value. (https://github.com/mdp/rotp/commit/15d5104e3cb99f97d36c772f8f09cf7e2e77de20).
Impact
CVE-2024-8796 has a CVSS score of 5.3 (Medium). The vector is network-reachable, low privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (6.0.0); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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Devise-Two-Factor should be upgraded to version v6.0.0 as soon as possible. After upgrading, the length of shared secrets and TOTP URLs generated by the library will increase since the new shared secrets will be longer.
If upgrading is not possible, you can override the default otp_secret_length attribute in the model when configuring two_factor_authenticable and set it to a value of at least 26 to ensure newly generated shared secrets are at least 128-bits long.
After upgrading or implementing the workaround, applications using Devise-Two-Factor may wish to migrate users to the new OTP length to provide increased protection for those accounts. Turning off OTP for users by setting otp_required_for_login to false is not recommended since it would leave accounts unprotected. However, you may wish to implement application logic that checks the length of a user's shared secret and prompts users to re-enroll in OTP.
Frequently Asked Questions
- What is CVE-2024-8796? CVE-2024-8796 is a medium-severity security vulnerability in devise-two-factor (rubygems), affecting versions >= 4.0.0, < 6.0.0. It is fixed in 6.0.0.
- How severe is CVE-2024-8796? CVE-2024-8796 has a CVSS score of 5.3 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of devise-two-factor are affected by CVE-2024-8796? devise-two-factor (rubygems) versions >= 4.0.0, < 6.0.0 is affected.
- Is there a fix for CVE-2024-8796? Yes. CVE-2024-8796 is fixed in 6.0.0. Upgrade to this version or later.
- Is CVE-2024-8796 exploitable, and should I be worried? Whether CVE-2024-8796 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2024-8796 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2024-8796? Upgrade
devise-two-factorto 6.0.0 or later.