Skip to main content
HIGH

CVE-2021-28651

CVSS v3

7.5

HIGH

EPSS Score

7.4 %

exploit probability, as of 2026-10-19

CISA KEV

No

known exploited

Exploitation

—

SSVC status

Get an alert for each new CVE published for squid.

Set up CVE WatchFree account · no credit card

Affected and fixed versions

Packages from OSV.dev and products from the vendors' CSAF advisories.

version not verifiedVersions not verified: read as OSV.dev and the vendors publish them, not checked against each vendor's release list.

Packages

  • libecapAlmaLinux:8all versions · fixed in 1.0.1-2.module_el8.6.0+2741+01592ae8and 1 other package
  • squidAlmaLinux:8all versions · fixed in 7:4.15-3.module_el8.6.0+3010+383bc947.1

Vendor advisories

  • CVE-2021-28651 Red Hat Product Security51 products fixed · 4 known affected

    squid: denial of service in URN processing

    squid as a component of Red Hat Enterprise Linux 6 · squid.src as a component of Red Hat Enterprise Linux 6 · squid34 as a component of Red Hat Enterprise Linux 6

  • RHSA-2025:14414 Red Hat Product Security21 products fixed

    Red Hat Security Advisory: squid security update

  • RHSA-2021:4292 Red Hat Product Security30 products fixed

    Red Hat Security Advisory: squid:4 security, bug fix, and enhancement update

Full record on NVD

Description

An issue was discovered in Squid before 4.15 and 5.x before 5.0.6. Due to a buffer-management bug, it allows a denial of service. When resolving a request with the urn: scheme, the parser leaks a small amount of memory. However, there is an unspecified attack methodology that can easily trigger a large amount of memory consumption.

Technical details

Published
2021-05-27

Frequently asked questions

What is CVE-2021-28651?

An issue was discovered in Squid before 4.15 and 5.x before 5.0.6. Due to a buffer-management bug, it allows a denial of service. When resolving a request with the urn: scheme, the parser leaks a small amount of memory. However, there is an unspecified attack methodology that can easily trigger a large amount of memory consumption.

Is CVE-2021-28651 actively exploited?

Active exploitation of CVE-2021-28651 has not been confirmed. Its EPSS score was 7.4% on 2026-10-19, the estimated probability of exploitation in the next 30 days.

What is the CVSS score for CVE-2021-28651?

CVE-2021-28651 has a CVSS v3 base score of 7.5 (HIGH severity).

Running squid? Hear about its next vulnerability

CVE Watch matches each new CVE to the vendors and products you list (vendor and product, not the version) and puts it in your alerts with its KEV and EPSS status.

Get alerts for this productCISA KEV additions, October 2026Search CVEs

Already have an account? Open CVE WatchNo credit card required · No monthly cap on website lookups · 250 API requests/month

Go further

Related vulnerabilities

Same product first, then the same vendor advisory and the same publication week.

Back to CVE Database