How severe is CVE-2021-31806?

CVE-2021-31806 has a CVSS 3.x base score of 6.5, rated medium severity. It is exploitable over network with low attack complexity, requires low privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.

Is CVE-2021-31806 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 96% (100th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-31806?

CVE-2021-31806 primarily affects Squid-cache Squid. In total, 6 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2021-31806?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

When was CVE-2021-31806 published?

CVE-2021-31806 was published on 2021-05-27 and last updated on 2026-06-17.

CVE-2021-31806

CVE-2021-31806 is a medium-severity vulnerability in Squid-cache Squid with a CVSS 3.x base score of 6.5. Its EPSS exploit-prediction score of 96% places it in the 100th percentile, indicating an elevated likelihood of exploitation. The underlying weakness is classified as CWE-116.

Key facts

Severity: Medium (CVSS 3.x base score 6.5)
CVSS v2: 4.0
EPSS exploit prediction: 96% (100th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-116
Affected product: Squid-cache Squid
Published: 2021-05-27
Last modified: 2026-06-17

Description

An issue was discovered in Squid before 4.15 and 5.x before 5.0.6. Due to a memory-management bug, it is vulnerable to a Denial of Service attack (against all clients using the proxy) via HTTP Range request processing.

Frequently asked questions

What is CVE-2021-31806?: An issue was discovered in Squid before 4.15 and 5.x before 5.0.6. Due to a memory-management bug, it is vulnerable to a Denial of Service attack (against all clients using the proxy) via HTTP Range request processing.
How severe is CVE-2021-31806?: CVE-2021-31806 has a CVSS 3.x base score of 6.5, rated medium severity. It is exploitable over network with low attack complexity, requires low privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.
Is CVE-2021-31806 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 96% (100th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-31806?: CVE-2021-31806 primarily affects Squid-cache Squid. In total, 6 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2021-31806?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
When was CVE-2021-31806 published?: CVE-2021-31806 was published on 2021-05-27 and last updated on 2026-06-17.

References

Affected products (6)

cpe:2.3:a:squid-cache:squid:*:*:*:*:*:*:*:*
cpe:2.3:o:debian:debian_linux:9.0:*:*:*:*:*:*:*
cpe:2.3:o:debian:debian_linux:10.0:*:*:*:*:*:*:*
cpe:2.3:o:fedoraproject:fedora:33:*:*:*:*:*:*:*
cpe:2.3:o:fedoraproject:fedora:34:*:*:*:*:*:*:*
cpe:2.3:a:netapp:cloud_manager:-:*:*:*:*:*:*:*

More vulnerabilities in Squid-cache Squid

CVE-2025-62168 — Critical (CVSS 10.0): Squid is a caching proxy for the Web. In Squid versions prior to 7.2, a failure to redact HTTP authentication…
CVE-2020-15049 — Critical (CVSS 9.9): An issue was discovered in http/ContentLengthInterpreter.cc in Squid before 4.12 and 5.x before 5.0.3. A Request…
CVE-2020-11945 — Critical (CVSS 9.8): An issue was discovered in Squid before 5.0.2. A remote attacker can replay a sniffed Digest Authentication nonce to…
CVE-2019-12519 — Critical (CVSS 9.8): An issue was discovered in Squid through 4.7. When handling the tag esi:when when ESI is enabled, Squid calls…
CVE-2019-12524 — Critical (CVSS 9.8): An issue was discovered in Squid through 4.7. When handling requests from users, Squid checks its rules to see if the…
CVE-2019-12526 — Critical (CVSS 9.8): An issue was discovered in Squid before 4.9. URN response handling in Squid suffers from a heap-based buffer overflow.…

All CVEs affecting Squid-cache Squid →

Other CWE-116 vulnerabilities

CVE-2025-55730 — Critical (CVSS 10.0): XWiki Remote Macros provides XWiki rendering macros that are useful when migrating content from Confluence. Starting in…
CVE-2025-55729 — Critical (CVSS 10.0): XWiki Remote Macros provides XWiki rendering macros that are useful when migrating content from Confluence. Starting in…
CVE-2023-47143 — Critical (CVSS 10.0): IBM Tivoli Application Dependency Discovery Manager 7.3.0.0 through 7.3.0.10 is vulnerable to HTTP header injection,…
CVE-2023-26472 — Critical (CVSS 9.9): XWiki Platform is a generic wiki platform. Starting in version 6.2-milestone-1, one can execute any wiki content with…
CVE-2022-41934 — Critical (CVSS 9.9): XWiki Platform is a generic wiki platform offering runtime services for applications built on top of it. Any user with…
CVE-2022-36100 — Critical (CVSS 9.9): XWiki Platform Applications Tag and XWiki Platform Tag UI are tag applications for XWiki, a generic wiki platform.…

Browse all CWE-116 vulnerabilities →

Threat intelligence

Threat-intel indicators referencing this CVE:

200.89.159.59 (ipv4-addr)
192.3.127.40 (ipv4-addr)