Predictive Vulnerability Intelligence.

Product

  • Product
  • Pricing
  • Documentation

Company

  • About
  • Partnerships
  • Blog
  • Support

Legal

  • Terms
  • Privacy
  • Data Licensing

© 2026 FAUCET Technologies LLC. All rights reserved.

CVE-2021-31806

81
FAUCET Score

CVE-2021-31806 is a Denial of Service vulnerability affecting Squid versions before 4.15 and 5.x before 5.0.6, as well as products from Debian, Fedora Project, and NetApp that utilize Squid. This flaw stems from a memory-management bug triggered by HTTP Range request processing, which can disrupt proxy services for all clients. With a CVSS score of 6.5 (Medium), it can be exploited remotely with low privileges and no user interaction, leading to high availability impact. While not observed in active exploitation, a Metasploit module exists, and its high EPSS and FAUCET Risk scores indicate a significant potential for future exploitation, despite a lack of public discussion or media coverage.

Impacted Technologies

VendorProductVersion(s)CPE
< 4.15CPE matchmatch criteria
cpe:2.3:a:squid-cache:squid:*:*:*:*:*:*:*:*
>= 5.0, < 5.0.6CPE matchmatch criteria
cpe:2.3:a:squid-cache:squid:*:*:*:*:*:*:*:*
9.0CPE matchmatch criteria
cpe:2.3:o:debian:debian_linux:9.0:*:*:*:*:*:*:*
10.0CPE matchmatch criteria
cpe:2.3:o:debian:debian_linux:10.0:*:*:*:*:*:*:*
33CPE matchmatch criteria
cpe:2.3:o:fedoraproject:fedora:33:*:*:*:*:*:*:*

CVSS Data

CVSS version used by this source: 3.1

6.5MEDIUM

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
LOW
User Interaction
NONE
Scope
UNCHANGED
Confidentiality Impact
NONE
Integrity Impact
NONE
Availability Impact
HIGH
Exploitability Score
2.8
Impact Score
3.6
CvssVersion
3.1

Exploit Intelligence

EPSS Score
95.78%
Probability of exploitation in next 30 days
EPSS Percentile
99.9%
Percentile rank of EPSS score among Peer Group
As of 2026-07-27
Model: v2026.06.15
Metasploit: Squid Proxy Range Header DoS · May 27, 2021
This CVE's current EPSS score of 0.9578 is in the 100th percentile among its peer group of 21,974 CVEs.

Social Chatter

The average CVE in this peer group has 0.0 Twitter, 0.0 Reddit, 0.1 Bluesky, 0.0 Mastodon, and 0.1 GitHub mentions.

Media Mentions

No media coverage found for this CVE.

The average CVE in this peer group has 0.0 InfoSec Media, 0.0 Vendor Blog, and 0.0 Security Researcher mentions.

Remediation

Patch Available

Vendor Patches (2)

github_advisorypatch availablevia nvd_reference
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Enterprise Linux 8Fixed in: squid:4-8050020210618131503.b4937e53
View patch

Vendor Advisories (1)

redhatCVE-2021-31806Moderate

squid: improper input validation in HTTP Range header

May 10, 2021

References

seclists.org / fulldisclosure/2023/Oct/14
Mailing ListThird Party Advisory
github.com / squid-cache/squid/security/advisories/GHSA-pxwq-f3qr-w2xf
PatchThird Party Advisory
lists.debian.org / debian-lts-announce/2021/06/msg00014.html
Mailing ListThird Party Advisory
lists.fedoraproject.org / archives/list/package-announce%40lists.fedoraproject.org/message/LSQ3U54ZCNXR44QRPW3AV2VCS6K3TKCF
lists.fedoraproject.org / archives/list/package-announce%40lists.fedoraproject.org/message/T4EPIWUZDJAXADDHVOPKRBTQHPBR6H66
security.netapp.com / advisory/ntap-20210716-0007
Third Party Advisory
debian.org / security/2021/dsa-4924
Third Party Advisory
openwall.com / lists/oss-security/2023/10/11/3
Mailing ListThird Party Advisory
squid-cache.org / Versions/v4/changesets/squid-4-e7cf864f938f24eea8af0692c04d16790983c823.patch
PatchVendor Advisory