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No exploitation reportedFix available

CVE-2021-39275

No exploitation reported by the sources we read.

  • Published2021-09-16
  • Fixed in2.4.49
  • WeaknessCWE-787

Am I affected?

With a domain, we read the version its public headers and pages expose. A distribution build can carry the fix under an older number.

Description

ap_escape_quotes() may write beyond the end of a buffer when given malicious input. No included modules pass untrusted data to these functions, but third-party / external modules may. This issue affects Apache HTTP Server 2.4.48 and earlier.

Timeline

dates in UTC
  1. 2021-09-1615:15CVE publishedNVD
  2. 2026-10-2319:23EPSS crossed 10 %FIRST EPSS

Observed activity

isMalicious corpus · updated 2026-11-04 09:37 UTC
Indicators tagged with this CVE, per day0 indicators over 7 days
Block these indicators
  • Firewall list (EDL, text): https://api.ismalicious.com/edl/cve/CVE-2021-39275?format=txt
  • CSV export: https://api.ismalicious.com/edl/cve/CVE-2021-39275?format=csv
  • TAXII collection of exploited CVEs
  • The EDL and CSV take an API key on the Pro plan.

Versions per branch

NVD · OSV
Apache HTTP Server
BranchAffectedFixed in
2.4< 2.4.492.4.49
Debian debian linux
BranchAffectedFixed in
9.0= 9.0no fix published
10.0= 10.0no fix published
11.0= 11.0no fix published
Oracle instantis enterprisetrack
BranchAffectedFixed in
17.1= 17.1no fix published
17.2= 17.2no fix published
17.3= 17.3no fix published

8 more products in the sources.

as publishedRanges as NVD and OSV publish them; a distribution’s build can be fixed under an older number.

Distribution builds and vendor advisories

Packages from OSV.dev and products from the vendors' CSAF advisories.

version not verifiedVersions not verified: read as OSV.dev and the vendors publish them, not checked against each vendor's release list.

Packages

  • apacheMageia:8all versions · fixed in 2.4.49-1.mga8
  • apache2Ubuntu:Pro:16.04:LTSall versions · fixed in 2.4.18-2ubuntu3.17+esm2
  • apache2Ubuntu:Pro:14.04:LTSall versions · fixed in 2.4.7-1ubuntu4.22+esm2
  • apache2Ubuntu:20.04:LTSall versions · fixed in 2.4.41-4ubuntu3.5
  • apache2Ubuntu:18.04:LTSall versions · fixed in 2.4.29-1ubuntu4.17
  • apache2TuxCare:Ubuntu:16.04all versions · fixed in 2.4.18-2ubuntu3.19and 7 other packages
  • apache2SUSE:OpenStack Cloud Crowbar 9all versions · fixed in 2.4.23-29.80.1
  • apache2SUSE:OpenStack Cloud Crowbar 8all versions · fixed in 2.4.23-29.80.1

89 more package ranges on OSV.dev

Vendor advisories

  • RHSA-2022:7143 Red Hat Product Security27 products fixed

    Red Hat Security Advisory: Red Hat JBoss Core Services Apache HTTP Server 2.4.51 security update

  • RHSA-2022:7144 Red Hat Product Security1 product fixed

    Red Hat Security Advisory: Red Hat JBoss Core Services Apache HTTP Server 2.4.51 security update

  • RHSA-2022:6753 Red Hat Product Security36 products fixed

    Red Hat Security Advisory: httpd24-httpd security and bug fix update

Full record on NVD

Fix

  1. Update Apache HTTP Server to 2.4.49
  2. Vendor fix Red Hat Product Security RHSA-2022:7143 · 27 productsFor details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258 Applications using the APR libraries, such as httpd, must be restarted for this update to take effect. After installing the updated packages, the http…
  3. Vendor fix Red Hat Product Security RHSA-2022:7144 · 1 productFor details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258
  4. Vendor fix Red Hat Product Security RHSA-2022:6753 · 36 productsFor details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258 After installing the updated packages, the httpd daemon will be restarted automatically.
  5. Workaround from the vendor Red Hat Product Security RHSA-2022:7143 · 156 productsMitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base or stability.

Advisories and patches

Detection

Nuclei template
none so far
ProjectDiscovery
Exploit-DB
no entry
Exploit-DB
Proof-of-concept repositories
none listed
PoC-in-GitHub
Metasploit modules
none listed
Metasploit Framework

Sources

  • NVDCVSS 3.19.8read 2026-10-23
  • NVDCVSS 2.07.5read 2026-10-23
  • NVDweakness (CWE)CWE-787read 2026-10-23
  • FIRST EPSSEPSS score39.4 %read 2026-11-03
  • OSVaffected packages—

Identifiers

Technical details

CVSS v3 Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Published
2021-09-16
Last Modified
2026-06-17
NVD status
Analyzed

Frequently asked questions

What is CVE-2021-39275?

ap_escape_quotes() may write beyond the end of a buffer when given malicious input. No included modules pass untrusted data to these functions, but third-party / external modules may. This issue affects Apache HTTP Server 2.4.48 and earlier.

Is CVE-2021-39275 actively exploited?

Active exploitation of CVE-2021-39275 has not been confirmed. Its EPSS score was 39.4% on 2026-11-03, the estimated probability of exploitation in the next 30 days.

What is the CVSS score for CVE-2021-39275?

CVE-2021-39275 has a CVSS v3 base score of 9.8 (CRITICAL severity), with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.

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