How severe is CVE-2021-42013?

CVE-2021-42013 has a CVSS score of 9.8/10, rated CRITICAL. Immediate patching is strongly recommended.

Which packages are affected by CVE-2021-42013?

Affected package information for CVE-2021-42013 is not yet fully mapped. Check the official advisory links for details.

How do I fix CVE-2021-42013?

No fixed version has been published for CVE-2021-42013 yet. Monitor the advisory for updates, apply mitigations recommended by the vendor, and use O3 Security to track when a fix becomes available in your stack.

Is CVE-2021-42013 actively exploited in the wild?

Yes. There are 32 known exploit references for CVE-2021-42013, including 4 documented proof-of-concept exploits on Exploit-DB and 21 in-the-wild exploitations observed on GitHub and other sources. Treat this as actively exploitable and prioritize patching immediately. All exploit code should only be run in an isolated sandbox environment for research or authorized testing — never against production systems without explicit written authorization.

What is the EPSS score for CVE-2021-42013?

CVE-2021-42013 has an EPSS (Exploit Prediction Scoring System) score of 94.4%, placing it in the 100th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. A score above 50% indicates significantly elevated exploitation risk — immediate patching is strongly recommended.

Is CVE-2021-42013 in the CISA Known Exploited Vulnerabilities catalog?

Yes. CVE-2021-42013 (Apache HTTP Server Path Traversal Vulnerability) was added to CISA's Known Exploited Vulnerabilities (KEV) catalog on 2021-11-03. CISA required all US federal civilian agencies to remediate this vulnerability by 2021-11-17. The required action was: Apply updates per vendor instructions. This CVE has been used in known ransomware campaigns. Being listed in the KEV catalog is the strongest possible confirmation of active exploitation — treat this as a critical priority.

What type of vulnerability is CVE-2021-42013?

CVE-2021-42013 is classified as Path Traversal (CWE-22). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation. This is a high-impact weakness class that often enables remote code execution or data exposure.

Is there exploit tooling available for CVE-2021-42013?

A Nuclei detection template exists for CVE-2021-42013, meaning automated scanners can fingerprint it. Public exploit tooling significantly increases real-world risk — prioritize patching and ensure detection coverage. Exploit tooling should only ever be used in isolated, authorized testing environments.

When was CVE-2021-42013 published, and has it been updated?

CVE-2021-42013 was published on October 7, 2021 and was last updated on April 16, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

CISA KEV·Added 2021-11-03 — agencies required to remediate by 2021-11-17 · Ransomware

CVE-2021-42013

CRITICAL

Also known asBIT-apache-2021-42013

Published

Oct 7, 2021

Updated

Apr 16, 2026

Affected

0 pkgs

Patched

None yet

Exploits

32 known

EPSS Exploitation Probability

via FIRST.org ↗

94.4%probability of exploitation in next 30 days

Very High Risk100th percentile0.00%

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.

Description

It was found that the fix for CVE-2021-41773 in Apache HTTP Server 2.4.50 was insufficient. An attacker could use a path traversal attack to map URLs to files outside the directories configured by Alias-like directives. If files outside of these directories are not protected by the usual default configuration "require all denied", these requests can succeed. If CGI scripts are also enabled for these aliased pathes, this could allow for remote code execution. This issue only affects Apache 2.4.49 and Apache 2.4.50 and not earlier versions.

Exploits & PoCs

Research use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.

EDB-50406webappsmultiple✓ Verified

Apache HTTP Server 2.4.50 - Path Traversal & Remote Code Execution (RCE)

by Lucas Souza · Oct 13, 2021

Exploit-DB Source

EDB-50512webappsmultiple✓ Verified

Apache HTTP Server 2.4.50 - Remote Code Execution (RCE) (3)

by Valentin Lobstein · Nov 11, 2021

Exploit-DB Source

EDB-50446webappsmultiple

Apache HTTP Server 2.4.50 - Remote Code Execution (RCE) (2)

by ThelastVvV · Oct 25, 2021

Exploit-DB Source

Frequently Asked Questions

O3 Security · Impact-Aware SCA

Is CVE-2021-42013 in your stack?

O3 detects CVE-2021-42013 across dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.

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