CVE
Hono validation bypass in form validator
- Exploited
- No known exploitation
- Fix
- Fixed in 4.13.16
- Who is exposed
- Not reported
Do first: Upgrade to a fixed version: 4.13.16.
- Last modified
- Whether it needs action now or is a reference record, by fixed rules, with why. Last checked is when cve.now last re-read it.What do these mean? →
- Reference
- Last checked
- FIRST's estimate of the chance attackers exploit it in the next 30 days, updated daily.What do these mean? →
- 0.39% · 33rd percentile
- A 0-100 score for how much a CVE matters across the industry: exploitation, exposure, how widely the software is used, severity and whether a fix exists.What do these mean? →
- 45/100 · provisional
- The share of the registry's downloads of each affected package in the window that were versions inside the affected ranges. Downloads, not users or installs: CI runs and mirrors inflate the counts.
- 79% of hono downloads last week were affected versions (83.7M).npm, 105.3M downloads in the last 7 days, read Nov 8, 2026
- Whether working attack code is public (Exploit-DB, Metasploit, Nuclei or GitHub). Public code makes attacks easier.What do these mean? →
- None on Exploit-DB, Metasploit or GitHub
- Exploitation: none
- Automatable: yes
- Technical impact: partial
Summary
Hono, a Web application framework for JavaScript runtimes, has a flaw in its `validator('form')` check: multipart/form-data requests whose Content-Type carries an extra parameter or stray whitespace after a semicolon skip validation and reach the handler with an empty object. A remote, unauthenticated client can exploit this to bypass allow-list or required-field checks, but only where the application relies on that validator and its callback accepts an empty object.
Written by anthropic/claude-haiku-5.5 from the sources below. Verify against them.
Read the original description
Hono is a Web application framework that provides support for any JavaScript runtime. From 4.5.1 until 4.13.16, validator('form') uses a strict whole-header pattern that fails to recognize multipart/form-data when its Content-Type includes another legal parameter or extra whitespace after a semicolon. The validation callback receives an empty object even though c.req.parseBody() or c.req.formData() can still parse and expose all submitted fields to the handler. An unauthenticated client can therefore bypass allow-list or required-field checks when the application relies on the form validator and its callback accepts an empty object. application/x-www-form-urlencoded requests are not affected. This issue is fixed in version 4.13.16.
cve.now Index
- Exploitation0/40No signal
- Exposure20/25No login or user action needed per the CVSS vector, CISA rates it automatable · Unknown: No advisory context yet
- Reach20/20hono: 104.5M downloads a week
- Severity5.3/10CVSS 5.3
- No patch0/5No signal
What would change the score
- Would score about 90 if added to CISA KEV
- Would score about 85 if CISA's SSVC rates exploitation active
- Would score about 50 if advisories confirm default setups are exposed
Impact
What to do
Upgrade to a fixed version: 4.13.16.
Check your systems with an agent
Paste this into a coding or ops agent. It checks your systems read-only and reports a table per asset.
Check whether my systems are affected by CVE-2026-126356 (Hono: `validator('form')` skips validation for `multipart/form-data` requests with extra parameters), using the cve.now data below.
Rules: work read-only. Do not run exploit code, proof-of-concept scripts or scanners that send attack payloads, and do not change any configuration, package, image or deployment. Report findings only.
What cve.now has for CVE-2026-126356 (entry last updated 2026-11-13):
Affected:
- honojs hono: from 4.5.1, fixed in 4.13.16
- npm package hono: from 4.5.1, fixed in 4.13.16
Fixed versions: 4.13.16.
Setup: unknown whether the bug needs a non-default feature or setting. Check the advisory.
CISA KEV: CVE-2026-126356 is not listed as of cve.now's last read.
This KEV status is for CVE-2026-126356 only. If you also check another CVE, look up its own KEV status; never assume it from this one.
How to check:
- Packages (npm): find every lockfile in each project and run the stack.check operation of the cve.now MCP server (execute) on each one. Compare the resolved versions, not the ranges a manifest declares, with the affected versions above. Include transitive dependencies.
Verify against the linked advisories before concluding, and cite the date you read each one:
- https://github.com/honojs/hono/security/advisories/GHSA-4h7h-rv7c-7m2v
- https://github.com/honojs/hono/commit/d88fab372415277a9e540e895650943dd08eef4a
- https://github.com/honojs/hono/releases/tag/v4.13.16
Do not conclude an asset is unaffected unless you checked it and the evidence covers both its version and the conditions above. If you could not check something, mark it unknown and say what is missing.
Report a table with one row per asset and these columns: Asset | Version or build | Status (affected, fixed, not applicable, unknown) | Compensating controls | Exposure (internet-facing, internal, none) | Evidence | Next action.
Entry: https://cve.now/CVE-2026-126356
For follow-up questions, use the cve.now MCP server at https://mcp.cve.now/mcp (no authentication), for example execute with name cve.get and arguments {"id": "CVE-2026-126356"}.Timeline
- CVE published
- First seen by cve.now1 day
- CISA SSVC assessment
Exploitation: none · Automatable: yes · Technical impact: partial
- Record last updated
Affected versions
- honojs hono
From 4.5.1 · fixed in 4.13.16
- hononpm
From 4.5.1 · fixed in 4.13.16
Fixed in 4.13.16 (released Nov 1, 2026, 11 days before disclosure).
The latest release, 4.13.17, is not affected.
Evidence 5
Vendor advisory · 1
Establishes: Affected and fixed versions.
- Advisory
CVE record · 2
Establishes: The identifier and description.
- Record
- Record
Other links · 2
- Repository
- Repository
Corrections
None so far.
Something wrong on this page? Report an error. Every fix is listed here.
Questions about CVE-2026-126356
Is CVE-2026-126356 being exploited?
It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.Source: cve.now feed data
Which versions are affected by CVE-2026-126356?
hono: from 4.5.1 before 4.13.16. hono (npm): from 4.5.1 before 4.13.16.Source: cve.now feed data
How do I fix CVE-2026-126356?
Upgrade to a fixed version: 4.13.16.Source: cve.now feed data