CVE-2026-42084

The OpenC3 password change functionality allows a user to change their password without providing the old password, by accepting a valid session token instead. In assumed breach scenarios, this behaviour can be exploited by an attacker who has already obtained a valid session token, to gain persistence in hijacked account (including admin) and prevent legitimate users from accessing the account.

Details

The design flaw in authentication model (authentication.rb) allows for interchangeable use of password and session tokens for user authentication As old tokens are not revoked upon password reset, an attacker who has obtained a valid session token can continue to authenticate and change the account’s password even after the victim resets it, thereby maintaining persistent control over the compromised account.

PoC

1. Attacker is logged in user account with hijacked valid session token, but not knowing the actual password
2. Legitimate user, as preventive action, changes his password (password123) using old password (password), that he knows, then establishes new session
3. Attacker issues another password change request (in web proxy like Burp) supplying his still valid token as old_password, changing it to attacker-password, from this point preventing any other legitimate users from accessing account

Persistence of an attacker who obtained valid session token and preventing legitimate users from account access

CVE-2026-42084 has a CVSS score of 8.1 (High). 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 (6.10.5, 7.0.0-rc3); upgrading removes the vulnerable code path.

Kodem intelligence

1. What is CVE-2026-42084? CVE-2026-42084 is a high-severity security vulnerability in openc3 (rubygems), affecting versions < 6.10.5. It is fixed in 6.10.5, 7.0.0-rc3.
2. How severe is CVE-2026-42084? CVE-2026-42084 has a CVSS score of 8.1 (High). 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.
3. Which versions of openc3 are affected by CVE-2026-42084? openc3 (rubygems) versions < 6.10.5 is affected.
4. Is there a fix for CVE-2026-42084? Yes. CVE-2026-42084 is fixed in 6.10.5, 7.0.0-rc3. Upgrade to this version or later.
5. Is CVE-2026-42084 exploitable, and should I be worried? Whether CVE-2026-42084 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
6. What actually determines whether CVE-2026-42084 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.
7. How do I fix CVE-2026-42084?
   • Upgrade openc3 to 6.10.5 or later
   • Upgrade openc3 to 7.0.0-rc3 or later