CVE-2021-28170
MEDIUMCVE-2021-28170 is a medium-severity (CVSS 5.3) Improper Input Validation vulnerability in com.sun.el:el-ri. 2 public exploit references exist, so weaponization risk is real. O3 Security confirms whether CVE-2021-28170 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
Improper Input Validation in Jakarta Expression Language
Real-World Exposure
com.sun.el:el-ri☕org.glassfish:jakarta.el☕org.glassfish:javax.elReal-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
In the Jakarta Expression Language implementation 3.0.3 and earlier, a bug in the ELParserTokenManager enables invalid EL expressions to be evaluated as if they were valid.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| ☕Maven | com.sun.el:el-ri | all versions | 3.0.4 |
| ☕Maven | org.glassfish:jakarta.el | all versions | 3.0.4 |
| ☕Maven | org.glassfish:javax.el | 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 com.sun.el:el-ri. 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 com.sun.el:el-ri to 3.0.4 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-28170 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-2021-28170 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-2021-28170. 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-2021-28170 in your dependencies?
O3 detects CVE-2021-28170 across Maven dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.