CVE-2026-42084 is a high-severity (CVSS 8.1) CWE-620 vulnerability in openc3. A fix is available for openc3 — see the affected versions and patch details below.
OpenC3 COSMOS: Hijacked session token can be used to reset password for persistence
Exploitation Status
Proof-of-concept exploit code exists
- CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.
- A successful exploit gives an attacker total control of the affected component, not partial access.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-42084.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
CVE-2026-42084 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 377,636 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
openc3💎openc3Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects RubyGems packages — download data is not available via public APIs for these ecosystems.
Description
Summary
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
- Attacker is logged in user account with hijacked valid session token, but not knowing the actual password
- Legitimate user, as preventive action, changes his password (password123) using old password (password), that he knows, then establishes new session
- 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 <img width="912" height="479" alt="image" src="https://github.com/user-attachments/assets/d27b5980-0326-40f8-bb39-657d7b1c95a0" />
Impact
Persistence of an attacker who obtained valid session token and preventing legitimate users from account access
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 💎RubyGems | openc3 | all versions | 6.10.5bundle update openc3 --conservative |
| 💎RubyGems | openc3 | ≥ 7.0.0.pre.rc1&&< 7.0.0-rc3 | 7.0.0-rc3bundle update openc3 --conservative |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for openc3, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update openc3 to 6.10.5 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-42084 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2026-42084 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2026-42084. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2026-42084 in your dependencies?
O3 Security finds CVE-2026-42084 across RubyGems dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.