CVE-2021-21265VulnerabilityPublished 10 Mar 2021Updated 29 May 2025

CVE-2021-21265: octobercms october · Improper Neutralization of HTTP Headers for Scripting Syntax

Affects octobercms octoberSource CVE Database V5

Not known to be exploited · CVSS 6.8 Medium : upgrade to 1.1.2 when convenient.

Data as of 26 Oct 2026, 06:26 UTC

CVSS 3.1 base score

6.8Medium

How severe the flaw is on the 0–10 CVSS scale.

EPSS: 1.7% chance of exploitation in 30 days – higher than 77% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in 1.1.2

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

Attack Vector: Network
Attack Complexity: High
Privileges Required: None
User Interaction: None
Scope: Changed
Confidentiality: None
Integrity: High
Availability: None

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: High: A successful attack depends on conditions beyond the attacker's control. That is, a successful attack cannot be accomplished at will, but requires the attacker to invest in some measurable amount of effort in preparation or execution against the vulnerable component before a successful attack can be expected. For example, a successful attack may require an attacker to: gather knowledge about the environment in which the vulnerable target/component exists; prepare the target environment to improve exploit reliability; or inject themselves into the logical network path between the target and the resource requested by the victim in order to read and/or modify network communications (e.g., a man in the middle attack).
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Changed: An exploited vulnerability can affect resources beyond the security scope managed by the security authority of the vulnerable component. In this case, the vulnerable component and the impacted component are different and managed by different security authorities.
Confidentiality: None: There is no loss of confidentiality within the impacted component.
Integrity: High: There is a total loss of integrity, or a complete loss of protection. For example, the attacker is able to modify any/all files protected by the impacted component. Alternatively, only some files can be modified, but malicious modification would present a direct, serious consequence to the impacted component.
Availability: None: There is no impact to availability within the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 10 Mar 2021
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 2026-10-26.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, or CISA SSVC reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Upgrade octobercms/october to 1.1.2.

Affected software

Product	Affected	Fixed in
Packagistoctobercms/october`pkg:composer/octobercms/october`Other threats	Affected <1.1.2	Fixed in 1.1.2

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

European organizations should take the following specific actions to mitigate this vulnerability: 1) Upgrade all October CMS instances to version 1.1.2 or later, where the trusted hosts feature is implemented. 2) Review and correct server configurations to ensure that HTTP requests are routed only to intended hosts, preventing arbitrary Host header routing. 3) Configure the cms.linkPolicy setting to 'force' as a temporary workaround if immediate upgrading is not feasible, restricting link generation to trusted hosts. 4) Implement strict input validation and sanitization for HTTP headers at the web server or application firewall level to detect and block suspicious Host header values. 5) Monitor web server logs for anomalous Host header values or unusual request patterns that could indicate attempted exploitation. 6) Educate development and operations teams about the risks of Host header manipulation and ensure secure deployment practices that avoid routing all requests indiscriminately. These measures go beyond generic patching by addressing the root cause in server configuration and application behavior.

Description

October is a free, open-source, self-hosted CMS platform based on the Laravel PHP Framework. In October before version 1.1.2, when running on poorly configured servers (i.e.the server routes any request, regardless of the HOST header to an October CMS instance) the potential exists for Host Header Poisoning attacks to succeed. This has been addressed in version 1.1.2 by adding a feature to allow a set of trusted hosts to be specified in the application. As a workaround one may set the configuration setting cms.linkPolicy to force.

Impact

For European organizations using October CMS versions prior to 1.1.2, this vulnerability poses a moderate risk primarily to the integrity of web applications. Successful exploitation could allow attackers to poison HTTP headers, potentially leading to cache poisoning or manipulation of password reset links, which could facilitate unauthorized account access or phishing attacks. While confidentiality and availability are not directly impacted, the integrity compromise can undermine trust in the affected web services and lead to reputational damage. Organizations with publicly accessible October CMS installations on poorly configured servers are particularly at risk. Given the widespread use of CMS platforms in Europe across sectors such as government, education, and small to medium enterprises, the vulnerability could be leveraged to target these entities, especially if they have not applied the patch or implemented the recommended host validation. The lack of known exploits reduces immediate risk but does not eliminate the threat, as attackers may develop exploits targeting misconfigured deployments.

CWE-644Improper Neutralization of HTTP Headers for Scripting Syntax (opens in a new tab)
Variant weaknessLikelihood of exploit: HighOWASP Top 10 A05:2025: Injection (opens in a new tab)
The product does not neutralize or incorrectly neutralizes web scripting syntax in HTTP headers that can be used by web browser components that can process raw headers, such as Flash.
Architecture and Design
Perform output validation in order to filter/escape/encode unsafe data that is being passed from the server in an HTTP response header.
Architecture and Design
Disable script execution functionality in the clients' browser.
OWASP Cheat Sheets
Content Security Policy (opens in a new tab)
Injection Prevention (opens in a new tab)
SQL Injection Prevention (opens in a new tab)
Injection Prevention in Java (opens in a new tab)
Query Parameterization (opens in a new tab)
OWASP ASVS 4.0.3
V14.4.6 (opens in a new tab)
V14.4.4 (opens in a new tab)
V14.4.2 (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 7 Jul 2025, 21:58 UTC

WeaknessesCWE-644

Technical details

References

Community reviews

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