EUVD-2026-38443
GHSA-55cm-p4ww-685g
Severity by source
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Network-reachable with no auth needed; integrity impact omitted because header injection was not confirmed; availability is Low due to runtime errors.
Primary rating from Vendor (VulnCheck).
CVSS VectorVendor: VulnCheck
Lifecycle Timeline
3Blast Radius
ecosystem impact- 66 npm packages depend on hono (49 direct, 17 indirect)
Ecosystem-wide dependent count for version 4.12.12.
DescriptionCVE.org
Hono before 4.12.12 does not validate cookie names on the write path in the setCookie(), serialize(), and serializeSigned() functions, allowing invalid characters such as control characters (e.g. \r or \n) when an application passes a user-controlled cookie name. This can produce malformed Set-Cookie header values. In modern runtimes such as Node.js and Cloudflare Workers, such invalid header values are rejected and cause a runtime error before the response is sent, so header injection or response splitting could not be reproduced; the issue primarily affects correctness and robustness, resulting in runtime errors (availability) rather than confirmed header injection.
AnalysisAI
Missing cookie name validation on the write path in Hono's setCookie(), serialize(), and serializeSigned() functions allows user-controlled input containing CRLF control characters to produce malformed Set-Cookie headers. Affected are all Hono npm releases before 4.12.12. In practice, modern runtimes including Node.js and Cloudflare Workers reject the malformed headers before they are transmitted, meaning confirmed impact is availability loss (runtime errors crashing the response) rather than header injection or response splitting - though theoretical risk exists on less-strict runtimes. No active exploitation is confirmed, and no public exploit code has been identified.
Technical ContextAI
Hono is a lightweight, TypeScript-first web framework designed for edge and serverless runtimes including Cloudflare Workers, Deno, Bun, and Node.js. The vulnerability is rooted in CWE-113 (Improper Neutralization of CRLF Sequences in HTTP Headers), a class of flaw where unvalidated newline characters allow an attacker to inject additional headers or split HTTP responses. The affected code paths - setCookie(), serialize(), and serializeSigned() - handle cookie serialization and generate Set-Cookie header values. The library validates certain cookie attributes (domain, path) on the write path but omits validation of the cookie name itself, creating an asymmetry between the stricter read/parse path and the permissive write path. When a CRLF sequence (e.g., \r or \n) is embedded in a cookie name, the resulting Set-Cookie header value can contain what appears to be an additional injected header line. The CPE cpe:2.3:a:hono:hono:*:*:*:*:*:*:*:* covers all Hono versions through the vulnerable range.
RemediationAI
Upgrade the Hono npm package to version 4.12.12 or later; this is the vendor-released patch confirmed by advisory GHSA-26pp-8wgv-hjvm and patch commit https://github.com/honojs/hono/commit/a586cd72e3f6122792e631ecf1817e5cabb803ec. As an immediate compensating control before patching, applications should sanitize or allowlist-validate any user-supplied values before passing them as cookie names to setCookie(), serialize(), or serializeSigned() - specifically rejecting input containing ASCII control characters (values 0x00-0x1F and 0x7F). This validation should occur at the application boundary before invoking Hono's cookie APIs. Note that relying solely on runtime rejection (as occurs in Node.js and Cloudflare Workers) is not a recommended long-term control, as it results in unhandled errors and broken responses rather than graceful handling.
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Same weakness CWE-113 – HTTP Response Splitting
View allSame technique Code Injection
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External POC / Exploit Code
Leaving vuln.today