VulnerabilityPublished 4 Mar 2026

CVE-2026-29086: honojs hono · Inappropriate Comment Style

Affects honojs honoSource CVE Database V5

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Not known to be exploited · CVSS 5.4 Medium : upgrade to 4.12.4 when convenient.

Data as of 30 Oct 2026, 11:52 UTC

CVSS 3.1 base score

5.4Medium

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

EPSS: 0.2% chance of exploitation in 30 days – higher than 13% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in 4.12.4

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

Attack Vector: Network
Attack Complexity: Low
Privileges Required: None
User Interaction: Required
Scope: Unchanged
Confidentiality: Low
Integrity: Low
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: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
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: Required: Successful exploitation of this vulnerability requires a user to take some action before the vulnerability can be exploited.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: Low: There is some loss of confidentiality. Access to some restricted information is obtained, but the attacker does not have control over what information is obtained, or the amount or kind of loss is limited. The information disclosure does not cause a direct, serious loss to the impacted component.
Integrity: Low: Modification of data is possible, but the attacker does not have control over the consequence of a modification, or the amount of modification is limited. The data modification does not have a direct, serious impact on 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 4 Mar 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: 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 30 Oct 2026.

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.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), or CISA SSVC or the CVSS exploit maturity 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 honojs hono to 4.12.4.

Affected software

Product	Affected	Fixed in
honojshono	Affected <4.12.4	Fixed in 4.12.4

AI-suggested

The most effective mitigation is to upgrade the honojs hono framework to version 4.12.4 or later, where the vulnerability has been patched. Organizations should audit their codebases and dependencies to identify usage of the setCookie() utility and ensure that untrusted input is never directly passed to cookie domain or path attributes without proper sanitization. Implement strict input validation and encoding on all user-supplied data used in cookie construction. Employ Content Security Policy (CSP) headers to reduce the impact of potential injection attacks. Monitor web application logs for suspicious cookie header manipulations or anomalies. Additionally, consider implementing web application firewalls (WAFs) with rules to detect and block malformed Set-Cookie headers containing unexpected delimiters or control characters. Educate developers on secure cookie handling practices and the risks of improper input validation in HTTP headers. Finally, conduct regular security testing, including fuzzing and penetration testing, to detect similar injection vulnerabilities in web application components.

Description

Hono is a Web application framework that provides support for any JavaScript runtime. Prior to version 4.12.4, the setCookie() utility did not validate semicolons (;), carriage returns (\r), or newline characters (\n) in the domain and path options when constructing the Set-Cookie header. Because cookie attributes are delimited by semicolons, this could allow injection of additional cookie attributes if untrusted input was passed into these fields. This issue has been patched in version 4.12.4.

Impact

The primary impact of this vulnerability is on the confidentiality and integrity of web session cookies. By injecting additional cookie attributes, an attacker could manipulate cookie behavior, potentially bypassing security controls such as HttpOnly or Secure flags, or altering cookie scope and expiration. This can lead to session hijacking, fixation, or cross-site scripting (XSS) attack facilitation. For organizations, this could result in unauthorized access to user accounts, data leakage, and erosion of user trust. While the vulnerability does not directly affect system availability, the indirect consequences of compromised sessions could disrupt business operations and lead to regulatory compliance issues, especially in sectors handling sensitive personal or financial data. Since honojs is a framework supporting any JavaScript runtime, the scope includes a broad range of web applications globally, increasing the potential attack surface. Organizations relying on vulnerable versions may face targeted attacks exploiting this flaw, particularly in environments where user input is not properly sanitized before being passed to setCookie().

References

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 4 Mar 2026, 22:33 UTC

WeaknessesCWE-1113

Technical details

References

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