# CVE-2021-42013: Apache HTTP Server Path Traversal Vulnerability

- Exploited (CISA KEV): yes, added 2021-11-03, known ransomware use
- Published: 2021-10-07
- CVSS: 9.8 CRITICAL (v3.1)
- EPSS: 100.0% (100th percentile)
- CWE: CWE-22

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.

## Edge WAF coverage (claimed by vendors, not measured)

| Vendor | Status | First rule | Days after publication |
|---|---|---|---|
| Cloudflare | Before feed history | — | — |
| AWS | No public claim | — | — |
| Microsoft Azure | No public claim | — | — |
| Google Cloud | Before feed history | — | — |
| Fastly | Before feed history | — | — |
| F5 | Rule published | 2024-03-12 | — |
| Akamai | No public source | — | — |
| OWASP CRS | Before feed history | — | — |

### F5

- 2024-03-12 · updated · rule 200007043
  > Updated: signature 200007043 "Directory Traversal attempt "../" (URI) (%%32%65%%32%65)" (Path Traversal, risk High), systems: Apache. References: CVE-2021-42013, CVE-2021-41773.
  Source: https://docs.cloud.f5.com/docs-v2/platform/changelogs/security-details-changelog

## Our test (measured)

- OWASP Core Rule Set 4.25.0, paranoia level 1, anomaly threshold 5, default CRS settings: error (0 of 3 requests blocked), template CVE-2021-42013, 2026-11-02
- OWASP Core Rule Set 4.25.0, paranoia level 2, anomaly threshold 5, default CRS settings: error (0 of 3 requests blocked), template CVE-2021-42013, 2026-11-02

"No public claim" means no vendor statement names this CVE; "Before feed history" means the CVE is older than the vendor feed. In both cases generic rules may still block it.

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