CVE
Hono cross-site scripting in the css helper
- 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? →
- 0.26% · 18th 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? →
- 30/100 · 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.
- 80% of hono downloads last week were affected versions (83.8M).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
Summary
Hono, a web application framework, has a flaw in its css helper where a closing style tag split between template text and an untrusted value is not escaped, so HTML injection is possible during server-side rendering. An attacker can reach it remotely without logging in, but a viewer must take some action, and the injected HTML or script can access information on the affected page.
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 3.12.0 until 4.13.16, the css helper in hono/css escapes interpolated string values separately and therefore fails to neutralize a closing style tag when < ends the template text or a preceding value and / begins the next attacker-controlled value. During server-side rendering, the combined output can close the <Style /> element early and cause the remainder of the interpolated value to be interpreted as HTML. Applications that place an untrusted string immediately after < in a css template, including adjacent untrusted interpolations, can expose viewers to attacker-controlled HTML or script and information accessible to that page. Other uses of the css helper are not affected. This issue is fixed in version 4.13.16.
cve.now Index
- Exploitation?/40Unknown. No CISA SSVC exploitation rating yet
- Exposure7/25Reachable over the network without a login · Unknown: No advisory context yet
- Reach20/20hono: 104.5M downloads a week
- Severity3.4/10CVSS 3.4
- No patch0/5No signal
What would change the score
- Would score about 85 if added to CISA KEV
- Would score about 80 if CISA's SSVC rates exploitation active
- Would score about 45 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-2026-126359 (Hono: `css` helper does not escape a closing tag split between the template and an interpolated value, allowing HTML injection), 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-2026-126359 (entry last updated 2026-11-12):
Affected:
- honojs hono: from 3.12.0, fixed in 4.13.16
- npm package hono: from 3.12.0, 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-2026-126359 is not listed as of cve.now's last read.
This KEV status is for CVE-2026-126359 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-3gg2-335m-rxc6
- https://github.com/honojs/hono/commit/15bbd96ad1b62a0b189db4fd8dc7bf8ef280c513
- 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-2026-126359
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-2026-126359"}.Timeline
- CVE published
- First seen by cve.now
Affected versions
- honojs hono
From 3.12.0 · fixed in 4.13.16
- hononpm
From 3.12.0 · 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-2026-126359
Is CVE-2026-126359 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-2026-126359?
hono: from 3.12.0 before 4.13.16. hono (npm): from 3.12.0 before 4.13.16.Source: cve.now feed data
How do I fix CVE-2026-126359?
Upgrade to a fixed version: 4.13.16.Source: cve.now feed data