CVE-2021-39275: ap_escape_quotes buffer overflow
Vulnerability summary
CVE-2021-39275 is a critical (CVSS 9.8) Out-of-bounds Write vulnerability in apache software foundation apache http server. EPSS estimates a 39.40% chance of exploitation in the next 30 days, higher than 98.6% of scored vulnerabilities.
Severe, CVSS 9.8 (NVD); no exploitation reported by the 5 checked sources; EPSS 39% (FIRST, 03-11-2026)
Source freshness unavailable
How is this decided?Advisory lineage
Upstream 0 · Downstream 14 · Duplicates 1 · Related 7Timeline
- 16-09-2021PublishedVulnerability first disclosed.
- 04-08-2024Last modifiedVulnerability information updated.
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.
CVSS metrics
5 scores · 4 sources · 2 versions- OSV · AlpineEcosystem advisory · calculated9.8CriticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
- OSV · UbuntuEcosystem advisory · calculated9.8CriticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
- OSV · DebianEcosystem advisory · calculated9.8CriticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
EPSS trend
Probability
39.40%
Chance of exploitation in the next 30 days
Percentile
99%
Versus all other CVEs
30-day change
No change 0.00 pp
From 39.40% on 04-10-2026
Known exploited
Compare KEV catalogs
CISA KEVNot in the CISA KEV catalog.
ENISA CNWNot in the ENISA CNW catalog.
CIRCLNot in the CIRCL catalog.
Public exploits
0 foundNo public exploits indexed.
Weaknesses
CWE · root causeAffected systems
Known conditions: network-reachable, no authentication, no user interaction (CVSS vector). Other conditions: not stated in public data.
Netapp3 products
Oracle3 products
- http_server12.2.1.3.0 | 12.2.1.4.0
- instantis_enterprisetrack17.1 | 17.2 | 17.3
- zfs_storage_appliance_kit8.8
Debian2 products
- apache2< 2.4.49-1
- debian_linuxEOL9.0 | 10.0 | 11.0
Suse2 products
- apache2&distro=SUSE Linux Enterprise Point of Sale 11 SP3< 2.2.34-70.38.1
- apache2&distro=SUSE Linux Enterprise Server 11 SP4-LTSS< 2.2.34-70.38.1
Alpine1 product
- apache2< 2.4.49-r0
Apache1 product
- http_server< 2.4.49
Apache software foundation1 product
- apache http server≥ Apache HTTP Server 2.4, ≤ 2.4.48
Fedoraproject1 product
- fedoraEOL34 | 35
Siemens1 product
- sinema_server14.0
Ubuntu1 product
- apache2< 2.4.7-1ubuntu4.22+esm2 | < 2.4.18-2ubuntu3.17+esm2 | < 2.4.29-1ubuntu4.17 | < 2.4.41-4ubuntu3.5
10 vendors · 16 products
References
26 links
lists.debian.org/debian-lts-announce/2021/10/msg00001.htmlMailing ListX Refsource MLISTThird Party Advisory- tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-apache-httpd-2.4.49-VWL69sWQVendor AdvisoryX Refsource CISCOThird Party Advisory
