CVE-2019-11881 is a medium-severity (CVSS 4.7) vulnerability in github.com/rancher/rancher. 3 public exploit references exist, so weaponization risk is real. No vendor fix is recorded yet; mitigation options are listed below.
Rancher Login Parameter Can Be Edited
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-2019-11881 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 378,156 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
github.com/rancher/rancherReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Go packages — download data is not available via public APIs for these ecosystems.
Description
A vulnerability exists in Rancher 2.1.4 in the login component, where the errorMsg parameter can be tampered to display arbitrary content, filtering tags but not special characters or symbols. There's no other limitation of the message, allowing malicious users to lure legitimate users to visit phishing sites with scare tactics, e.g., displaying a "This version of Rancher is outdated, please visit https://malicious.rancher.site/upgrading" message.
PoC
- Access the following endpoint on any Rancher instance up to 2.1.4:
https://RANCHER:PORT/login?errorMsg=%68%74%74%70%73%3a%2f%2f%77%77%77%2e%6f%77%61%73%70%2e%6f%72%67%2f%69%6e%64%65%78%2e%70%68%70%2f%57%65%62%5f%50%61%72%61%6d%65%74%65%72%5f%54%61%6d%70%65%72%69%6e%67
It will display a link to OWASP Wiki explaining Web Parameter Tampering.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐹Go | github.com/rancher/rancher | all versions | No fix |
Research use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/rancher/rancher, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Remediation status
No patched version of github.com/rancher/rancher has shipped for CVE-2019-11881 yet. Where your build allows, override or pin the dependency away from the vulnerable range, and apply any maintainer-recommended mitigation.
Mitigate without a patch
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-2019-11881 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2019-11881. 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-2019-11881 in your dependencies?
O3 Security finds CVE-2019-11881 across Go dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.