CVE-2024-38475: Apache HTTP Server Improper Escaping of Output Vulnerability

Should you act?

Exploited: patch now if you run it

CISA has confirmed exploitation in the wild. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.

• Yes, if you run Apache HTTP Server. CISA added this CVE to its Known Exploited Vulnerabilities catalog on 2025-05-01, which means there is reliable evidence of exploitation in the wild. US federal agencies must remediate by 2025-05-22; treat that as the outer limit, not the target.
• EPSS 100.0%, percentile 100.0: FIRST’s model estimates a 100.0% chance of exploitation activity in the next 30 days, higher than 100.0% of all scored CVEs (very high). EPSS is a probability, not a verdict.
• Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.

What it is

Improper escaping of output in modrewrite in Apache HTTP Server 2.4.59 and earlier allows an attacker to map URLs to filesystem locations that are permitted to be served by the server but are not intentionally/directly reachable by any URL, resulting in code execution or source code disclosure. Substitutions in server context that use a backreferences or variables as the first segment of the substitution are affected. Some unsafe RewiteRules will be broken by this change and the rewrite flag "UnsafePrefixStat" can be used to opt back in once ensuring the substitution is appropriately constrained.

CISA’s summary

Apache HTTP Server contains an improper escaping of output vulnerability in mod_rewrite that allows an attacker to map URLs to filesystem locations that are permitted to be served by the server but are not intentionally/directly reachable by any URL, resulting in code execution or source code disclosure.

Weakness type: CWE-116.

Product: Apache HTTP Server · Assigned by: apache · Published: 2024-07-01

Affected and fixed versions

Severity scores

• Attack vector: network (remotely reachable)
• Attack complexity: low
• Privileges required: none (no login)
• User interaction: none
• Scope: unchanged

CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.

Exploitation and urgency

• CISA KEV: added 2025-05-01; federal due date 2025-05-22. Known ransomware use: Unknown.
• CISA required action: Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.
• CISA SSVC assessment: exploitation active, automatable yes, technical impact total.
• FIRST EPSS (model of 2026-10-21): 99.96% probability of exploitation activity in the next 30 days; percentile 100.0.

Timeline

• 2024-07-01 — CVE record published by apache
• 2025-05-01 — Added to CISA’s Known Exploited Vulnerabilities catalog
• 2025-05-22 — CISA remediation deadline for US federal agencies
• 2025-11-03 — CVE record last updated

Sources and references

Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.

Vendor and project advisories, patches

1. Vendor advisory (httpd.apache.org) httpd.apache.org

Vulnerability records

1. CVE.org record CVE-2024-38475 cve.org
2. NVD entry CVE-2024-38475 nvd.nist.gov

Government

1. CISA Known Exploited Vulnerabilities catalog entry cisa.gov

Other references from the CVE record and advisory

1. security.netapp.com security.netapp.com
2. blackhat.com blackhat.com
3. github.com github.com
4. openwall.com openwall.com
5. psirt.global.sonicwall.com psirt.global.sonicwall.com

All exploited Apache vulnerabilities · Today’s Security Digest