How severe is CVE-2021-39275?

CVE-2021-39275 has a CVSS 3.x base score of 9.8, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.

Is CVE-2021-39275 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 36% (98th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-39275?

CVE-2021-39275 primarily affects Apache Http Server. In total, 17 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2021-39275?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.

When was CVE-2021-39275 published?

CVE-2021-39275 was published on 2021-09-16 and last updated on 2026-06-17.

CVE-2021-39275

CVE-2021-39275 is a critical-severity vulnerability in Apache Http Server with a CVSS 3.x base score of 9.8. Its EPSS exploit-prediction score of 36% places it in the 98th percentile, indicating an elevated likelihood of exploitation. The underlying weakness is classified as CWE-787.

Key facts

Severity: Critical (CVSS 3.x base score 9.8)
CVSS v2: 7.5
EPSS exploit prediction: 36% (98th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-787
Affected product: Apache Http Server
Published: 2021-09-16
Last modified: 2026-06-17

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.

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.
How severe is CVE-2021-39275?: CVE-2021-39275 has a CVSS 3.x base score of 9.8, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.
Is CVE-2021-39275 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 36% (98th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-39275?: CVE-2021-39275 primarily affects Apache Http Server. In total, 17 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2021-39275?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.
When was CVE-2021-39275 published?: CVE-2021-39275 was published on 2021-09-16 and last updated on 2026-06-17.

References

Affected products (17)

cpe:2.3:a:apache:http_server:*:*:*:*:*:*:*:*
cpe:2.3:o:fedoraproject:fedora:34:*:*:*:*:*:*:*
cpe:2.3:o:fedoraproject:fedora:35:*:*:*:*:*:*:*
cpe:2.3:o:debian:debian_linux:9.0:*:*:*:*:*:*:*
cpe:2.3:o:debian:debian_linux:10.0:*:*:*:*:*:*:*
cpe:2.3:o:debian:debian_linux:11.0:*:*:*:*:*:*:*
cpe:2.3:a:netapp:cloud_backup:-:*:*:*:*:*:*:*
cpe:2.3:a:netapp:clustered_data_ontap:-:*:*:*:*:*:*:*
cpe:2.3:a:netapp:storagegrid:-:*:*:*:*:*:*:*
cpe:2.3:a:oracle:http_server:12.2.1.3.0:*:*:*:*:*:*:*
cpe:2.3:a:oracle:http_server:12.2.1.4.0:*:*:*:*:*:*:*
cpe:2.3:a:oracle:instantis_enterprisetrack:17.1:*:*:*:*:*:*:*
cpe:2.3:a:oracle:instantis_enterprisetrack:17.2:*:*:*:*:*:*:*
cpe:2.3:a:oracle:instantis_enterprisetrack:17.3:*:*:*:*:*:*:*
cpe:2.3:a:oracle:zfs_storage_appliance_kit:8.8:*:*:*:*:*:*:*
cpe:2.3:a:siemens:sinec_nms:*:*:*:*:*:*:*:*
cpe:2.3:a:siemens:sinema_server:14.0:-:*:*:*:*:*:*

More vulnerabilities in Apache Http Server

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All CVEs affecting Apache Http Server →

Other CWE-787 (Out-of-bounds Write) vulnerabilities

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CVE-2025-24201 — Critical (CVSS 10.0): An out-of-bounds write issue was addressed with improved checks to prevent unauthorized actions. This issue is fixed in…
CVE-2024-42479 — Critical (CVSS 10.0): llama.cpp provides LLM inference in C/C++. The unsafe `data` pointer member in the `rpc_tensor` structure can cause…
CVE-2024-39791 — Critical (CVSS 10.0): Stack-based buffer overflow vulnerabilities affecting Vonets industrial wifi bridge relays and wifi bridge…

Browse all CWE-787 (Out-of-bounds Write) vulnerabilities →

Threat intelligence

Threat-intel indicators referencing this CVE:

50.255.62.89 (ipv4-addr)
147.15.15.226 (ipv4-addr)
218.4.91.163 (ipv4-addr)
45.84.120.3 (ipv4-addr)
79.137.34.248 (ipv4-addr)
61.76.112.4 (ipv4-addr)
60.199.224.2 (ipv4-addr)
46.253.45.10 (ipv4-addr)