CVE-2021-21265Network attack vector

Link poisoning via unvalidated Host header

Published Mar 10, 2021 · Updated May 29, 2025

Host header poisoning in October CMS before 1.1.2 allows remote attackers to alter generated links through a crafted Host header. Request handling trusted the HTTP Host header when the web server routed arbitrary hostnames to the application, and password-reset link generation reused that unvalidated value. Exploitation requires wildcard host routing; crafted reset links can direct recipients to an attacker-controlled host and compromise link integrity.

CVSS severity7.5
High
EPSS probability1.75%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Host header poisoning in October CMS before 1.1.2 allows remote attackers to alter generated links through a crafted Host header. Request handling trusted the HTTP Host header when the web server routed arbitrary hostnames to the application, and password-reset link generation reused that unvalidated value. Exploitation requires wildcard host routing; crafted reset links can direct recipients to an attacker-controlled host and compromise link integrity.

The record

CVE
CVE-2021-21265
Published
Mar 10, 2021
Updated
May 29, 2025
Vendor
October CMS
Product
October CMS
Classifications
CWE-644, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 10, 2021CVE publishedPublication date reported by the CVE source.
  2. May 29, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 1.1.2

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

October CMS · October CMSversion=< 1.1.2

Published CVSS scores

7.5NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
6.8GitHub Security AdvisoriesCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:H/A:N
4.3NVDAV:N/AC:M/Au:N/C:N/I:P/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-644Improper Neutralization of HTTP Headers for Scripting Syntax
T1190Exploit Public-Facing Application

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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