CVE-2021-26291
CRITICALCVE-2021-26291 is a critical-severity (CVSS 9.1) CWE-346 vulnerability in org.apache.maven:maven-compat. 1 public exploit reference exists, so weaponization risk is real. O3 Security confirms whether CVE-2021-26291 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
Origin Validation Error in Apache Maven
Real-World Exposure
org.apache.maven:maven-compat☕org.apache.maven:maven-coreReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Maven packages — download data is not available via public APIs for these ecosystems.
Description
Apache Maven will follow repositories that are defined in a dependency’s Project Object Model (pom) which may be surprising to some users, resulting in potential risk if a malicious actor takes over that repository or is able to insert themselves into a position to pretend to be that repository. Maven is changing the default behavior in 3.8.1+ to no longer follow http (non-SSL) repository references by default. More details available in the referenced urls. If you are currently using a repository manager to govern the repositories used by your builds, you are unaffected by the risks present in the legacy behavior, and are unaffected by this vulnerability and change to default behavior. See this link for more information about repository management: https://maven.apache.org/repository-management.html
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| ☕Maven | org.apache.maven:maven-compat | all versions | 3.8.1 |
| ☕Maven | org.apache.maven:maven-core | all versions | 3.8.1 |
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 org.apache.maven:maven-compat. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update org.apache.maven:maven-compat to 3.8.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-26291 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 pinpoints whether CVE-2021-26291 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to CVE-2021-26291. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Fixing This On Your OS
If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.
Frequently Asked Questions
Is CVE-2021-26291 in your dependencies?
O3 detects CVE-2021-26291 across Maven dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.