CVE-2021-39275 — Apache HTTP Server

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.

The record classifies CVE-2021-39275 under weakness class CWE-787. Its CVSS v3 base vector states that the flaw is reachable remotely over the network, needs no prior authentication, needs no user interaction, and has high impact on confidentiality, integrity, availability. 1 affected-product entry is recorded, across 1 vendor, listed below. The identifier was first published 1845 days ago.

Severity and exploitation probability

CVSS v3.1 base score: 9.8 — CRITICAL
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
EPSS (FIRST): 39.4% probability of exploitation in the next 30 days, higher than 98.4% of all scored CVEs
CISA KEV: Not listed in the CISA Known Exploited Vulnerabilities catalog
Threadlinqs priority: 10/10 — a Threadlinqs composite of the CVSS base score, the EPSS percentile and public exploit availability
Published: 2021-09-16, last modified 2024-08-04

Is CVE-2021-39275 being exploited?

Weaponised exploit code for CVE-2021-39275 is publicly available. 1 public proof-of-concept repository is tracked for this identifier.

trickest/cve (trickest)

Affected products and versions

Apache Software Foundation: Apache HTTP Server

How to fix CVE-2021-39275

The record marks a vendor fix as available for CVE-2021-39275. Patch reference: https://lists.apache.org/thread.html/r3925e167d5eb1c75def3750c155d753064e1d34a143028bb32910432%40%3Cusers.httpd.apache.org%3E. Vendor advisory: https://httpd.apache.org/security/vulnerabilities_24.html. Apply the vendor fix referenced above to every affected product listed in this record, then confirm the running version against the vendor advisory.

Threat activity tracking CVE-2021-39275

1 tracked threat in the Threadlinqs corpus references CVE-2021-39275, either in the campaign’s CVE list or as an indicator on the campaign record.

Russian Intelligence Services Hijack Unsecured IP Cameras Across NATO, EU and Ukraine to Surveil Weapons Deliveries (AIVD/MIVD Advisory, Censys Analysis) — HIGH · 2026-07-22

Sources

Enriched from CVE.org, NVD, FIRST EPSS, GitHub Security Advisories, public proof-of-concept repositories. Last verified by Threadlinqs on 2026-08-17. This product uses the NVD API but is not endorsed or certified by the NVD.

Vendor advisory and patch

Mailing list and disclosure

Other references

Showing 13 of 15 recorded references.