How severe is CVE-2021-28652?

CVE-2021-28652 has a CVSS 3.x base score of 4.9, rated medium severity. It is exploitable over network with low attack complexity, requires high privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.

Is CVE-2021-28652 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 4% (90th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-28652?

CVE-2021-28652 primarily affects Squid-cache Squid. In total, 5 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2021-28652?

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

When was CVE-2021-28652 published?

CVE-2021-28652 was published on 2021-05-27 and last updated on 2026-06-17.

CVE-2021-28652

CVE-2021-28652 is a medium-severity vulnerability in Squid-cache Squid with a CVSS 3.x base score of 4.9. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-401.

Key facts

Severity: Medium (CVSS 3.x base score 4.9)
CVSS v2: 4.0
EPSS exploit prediction: 4% (90th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-401
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 incorrect parser validation, it allows a Denial of Service attack against the Cache Manager API. This allows a trusted client to trigger memory leaks that. over time, lead to a Denial of Service via an unspecified short query string. This attack is limited to clients with Cache Manager API access privilege.

Frequently asked questions

What is CVE-2021-28652?: An issue was discovered in Squid before 4.15 and 5.x before 5.0.6. Due to incorrect parser validation, it allows a Denial of Service attack against the Cache Manager API. This allows a trusted client to trigger memory leaks that. over time, lead to a Denial of Service via an unspecified short query string. This attack is limited to clients with Cache Manager API access privilege.
How severe is CVE-2021-28652?: CVE-2021-28652 has a CVSS 3.x base score of 4.9, rated medium severity. It is exploitable over network with low attack complexity, requires high privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.
Is CVE-2021-28652 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 4% (90th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-28652?: CVE-2021-28652 primarily affects Squid-cache Squid. In total, 5 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2021-28652?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
When was CVE-2021-28652 published?: CVE-2021-28652 was published on 2021-05-27 and last updated on 2026-06-17.

References

Affected products (5)

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:*:*:*:*:*:*:*

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-401 (Missing Release of Memory after Effective Lifetime) vulnerabilities

CVE-2026-46289 — Critical (CVSS 9.8): In the Linux kernel, the following vulnerability has been resolved: lib/scatterlist: fix length calculations in…
CVE-2025-39948 — Critical (CVSS 9.8): In the Linux kernel, the following vulnerability has been resolved: ice: fix Rx page leak on multi-buffer frames The…
CVE-2025-21954 — Critical (CVSS 9.8): In the Linux kernel, the following vulnerability has been resolved: netmem: prevent TX of unreadable skbs Currently…
CVE-2024-57947 — Critical (CVSS 9.8): In the Linux kernel, the following vulnerability has been resolved: netfilter: nf_set_pipapo: fix initial map…
CVE-2024-56779 — Critical (CVSS 9.8): In the Linux kernel, the following vulnerability has been resolved: nfsd: fix nfs4_openowner leak when concurrent…
CVE-2024-36911 — Critical (CVSS 9.8): In the Linux kernel, the following vulnerability has been resolved: hv_netvsc: Don't free decrypted memory In CoCo…

Browse all CWE-401 (Missing Release of Memory after Effective Lifetime) vulnerabilities →

Threat intelligence

Threat-intel indicators referencing this CVE:

200.89.159.59 (ipv4-addr)
121.43.117.198 (ipv4-addr)
39.100.82.100 (ipv4-addr)
51.159.30.56 (ipv4-addr)
39.100.84.225 (ipv4-addr)
192.142.52.45 (ipv4-addr)
192.3.127.40 (ipv4-addr)
103.152.40.169 (ipv4-addr)