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Vulnerability record · CVE-2021-30641 · published 10 June 2021

CVE-2021-30641: Apache HTTP Server MergeSlashes OFF path matching flaw

Apache · Http Server

Apache HTTP Server versions 2.4.39 through 2.4.46 exhibit unexpected matching behavior when the MergeSlashes option is set to OFF. This can cause request paths to be matched differently than administrators intend, which matters because access control and routing rules may not apply as configured. The record gives no further detail on the exact matching discrepancy.

5.3 CVSS 3.1 Medium EPSS 53% · top 1.1%
5.3CVSS 3.1 base score, v2 5.0
53%EPSS exploitation probability, 30 days
NoNot in CISA KEV
6Affected product versions listed by NVD
24References
17 Jun 2026Last modified by NVD

Description

Apache HTTP Server versions 2.4.39 to 2.4.46 Unexpected matching behavior with 'MergeSlashes OFF'

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

Automated analysis

Generated by VULONE's analysis model from the NVD record, CISA KEV and EPSS data on 20 September 2026. Confidence: medium.

medium priorityMedium CVSS severity with limited integrity-only impact, but high EPSS and a widely deployed product warrant prompt patching.

What it is

Apache HTTP Server versions 2.4.39 through 2.4.46 exhibit unexpected matching behavior when the MergeSlashes option is set to OFF. This can cause request paths to be matched differently than administrators intend, which matters because access control and routing rules may not apply as configured. The record gives no further detail on the exact matching discrepancy.

Impact

An attacker may reach resources or code paths that the intended configuration was meant to block or route elsewhere, resulting in limited integrity impact. The CVSS vector shows no confidentiality or availability impact.

Attack surface

Reachable over the network via HTTP requests with no authentication and no user interaction required, per the CVSS vector AV:N/AC:L/PR:N/UI:N. It only applies to servers configured with MergeSlashes OFF.

Exploitation

Not listed in CISA KEV and no ransomware use documented, but EPSS is high at 0.526 (99th percentile), indicating elevated predicted exploitation likelihood. References are vendor advisories and distribution notices only, with no public exploit tags.

What to do

  • Upgrade Apache HTTP Server to a release after 2.4.46, which is the last affected version listed.
  • If upgrade is not immediate, review and avoid relying on MergeSlashes OFF for security-relevant path matching.
  • Audit access control and rewrite rules for assumptions about slash handling in request paths.
  • Apply the relevant distribution updates from Debian, Fedora, Gentoo, NetApp or Oracle advisories for packaged builds.

Detection

  • Review httpd configuration for MergeSlashes OFF and inventory affected servers.
  • Monitor access logs for request paths containing repeated or unusual slash sequences.
  • Compare logged request paths against expected routing and access control decisions to spot mismatches.

This assessment is produced automatically and is not human-reviewed. Verify against the vendor advisory before acting on it.

Affected products

6 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
http://httpd.apache.org/security/vulnerabilities_24.html Vendor Advisory
http://www.openwall.com/lists/oss-security/2021/06/10/8 Mailing ListThird Party Advisory
https://lists.apache.org/thread.html/r2b4773944d83d2799de9fbaeee7fe0f3fd72669467787e02f434cb10%40%3Cannounce.httpd.apach
https://lists.apache.org/thread.html/r7f2b70b621651548f4b6f027552f1dd91705d7111bb5d15cda0a68dd%40%3Cdev.httpd.apache.org
https://lists.apache.org/thread.html/re026d3da9d7824bd93b9f871c0fdda978d960c7e62d8c43cba8d0bf3%40%3Ccvs.httpd.apache.org Mailing ListRelease NotesVendor Advisory
https://lists.debian.org/debian-lts-announce/2021/07/msg00006.html Mailing ListThird Party Advisory
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/SPBR6WUYBJNACHKE65SPL7T
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/ZNCYSR3BXT36FFF4XTCPL3H
https://security.gentoo.org/glsa/202107-38 Third Party Advisory
https://security.netapp.com/advisory/ntap-20210702-0001/ Third Party Advisory
https://www.debian.org/security/2021/dsa-4937 Third Party Advisory
https://www.oracle.com/security-alerts/cpuoct2021.html Third Party Advisory
http://httpd.apache.org/security/vulnerabilities_24.html Vendor Advisory
http://www.openwall.com/lists/oss-security/2021/06/10/8 Mailing ListThird Party Advisory
https://lists.apache.org/thread.html/r2b4773944d83d2799de9fbaeee7fe0f3fd72669467787e02f434cb10%40%3Cannounce.httpd.apach
https://lists.apache.org/thread.html/r7f2b70b621651548f4b6f027552f1dd91705d7111bb5d15cda0a68dd%40%3Cdev.httpd.apache.org
https://lists.apache.org/thread.html/re026d3da9d7824bd93b9f871c0fdda978d960c7e62d8c43cba8d0bf3%40%3Ccvs.httpd.apache.org Mailing ListRelease NotesVendor Advisory
https://lists.debian.org/debian-lts-announce/2021/07/msg00006.html Mailing ListThird Party Advisory
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/SPBR6WUYBJNACHKE65SPL7T
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/ZNCYSR3BXT36FFF4XTCPL3H
https://security.gentoo.org/glsa/202107-38 Third Party Advisory
https://security.netapp.com/advisory/ntap-20210702-0001/ Third Party Advisory
https://www.debian.org/security/2021/dsa-4937 Third Party Advisory
https://www.oracle.com/security-alerts/cpuoct2021.html Third Party Advisory

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Source: NIST National Vulnerability Database (record CVE-2021-30641), CISA KEV, FIRST EPSS (scores of 2026-09-27). This page is refreshed as NVD updates the record.