CVE
Astro XSS in prism code block highlighting
- Exploited
- No known exploitation
- Fix
- Fixed in astro 7.4.3 · prism 4.1.2 · markdoc 2.1.2
- Who is exposed
- Not reported
Do first: Upgrade to a fixed version: astro 7.4.3 · prism 4.1.2 · markdoc 2.1.2.
- 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? →
- 0.17% · 6th 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? →
- 8/100 · provisional
- 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
Astro and the @astrojs/prism and @astrojs/markdoc packages can render embedded HTML and script from a code block labeled with an unsupported language, instead of showing it as text. An attacker with a low-privilege account can reach this remotely, but a user must take an action before the script runs.
Written by anthropic/claude-haiku-5.5 from the sources below. Verify against them.
Read the original description
Astro is a web framework for content-driven websites. Prior to @astrojs/prism 4.1.2, and from @astrojs/markdoc 0.3.0 until 2.1.2, runHighlighterWithAstro() returned code unchanged when Prism had no grammar for the requested language, and callers inserted that result as raw HTML. A code block labeled with an unsupported language could therefore render embedded HTML and script instead of displaying it as text. The Prism component was affected when applications supplied untrusted code with an unsupported or attacker-controlled lang, and the @astrojs/markdoc prism() extension was affected for less-trusted content authors even when Markdoc's ordinary HTML rendering was disabled. This issue is fixed in @astrojs/prism 4.1.2 and @astrojs/markdoc 2.1.2.
cve.now Index
- Exploitation?/40Unknown. No CISA SSVC exploitation rating yet
- Exposure3/25Reachable over the network · Unknown: No advisory context yet
- Reach?/20Unknown. No tracked technology or package matched
- Severity5.4/10CVSS 5.4
- No patch0/5No signal
What would change the score
- Would score about 63 if added to CISA KEV
- Would score about 58 if CISA's SSVC rates exploitation active
- Would score about 27 if advisories confirm default setups are exposed
What to do
Upgrade to a fixed version: astro 7.4.3 · prism 4.1.2 · markdoc 2.1.2.
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-2026-126365 (Astro: XSS via unescaped code for unsupported languages in @astrojs/prism), 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-2026-126365 (entry last updated 2026-11-12):
Affected:
- withastro astro: fixed in 7.4.3
- @astrojs prism: fixed in 4.1.2
- @astrojs markdoc: from 0.3.0, fixed in 2.1.2
Fixed versions: 7.4.3, 4.1.2, 2.1.2.
Setup: unknown whether the bug needs a non-default feature or setting. Check the advisory.
CISA KEV: CVE-2026-126365 is not listed as of cve.now's last read.
This KEV status is for CVE-2026-126365 only. If you also check another CVE, look up its own KEV status; never assume it from this one.
How to check:
- Installed software: check what is actually running, not what a repo declares. Read the version from each host, container image and Kubernetes node (the binary's version output, the OS package database, image layers), and check whether the conditions above hold there. Distribution packages may carry a backported fix under an older version number; confirm against the distribution's own advisory.
Verify against the linked advisories before concluding, and cite the date you read each one:
- https://github.com/withastro/astro/security/advisories/GHSA-ff38-p3qj-4pmf
- https://github.com/withastro/astro/commit/edfbf4ab34ff007ae8f7188af76a023a15c9443d
- https://github.com/withastro/astro/releases/tag/@astrojs/markdoc@2.1.2
- https://github.com/withastro/astro/releases/tag/@astrojs/prism@4.1.2
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-2026-126365
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-2026-126365"}.Timeline
- CVE published
- First seen by cve.now
Affected versions
- withastro astro
fixed in 7.4.3
- @astrojs prism
fixed in 4.1.2
- @astrojs markdoc
From 0.3.0 · fixed in 2.1.2
Evidence 6
Vendor advisory · 1
Establishes: Affected and fixed versions.
- Advisory
CVE record · 2
Establishes: The identifier and description.
- Record
- Record
Other links · 3
- Repository
- Repository
- Repository
Corrections
None so far.
Something wrong on this page? Report an error. Every fix is listed here.
Questions about CVE-2026-126365
Is CVE-2026-126365 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-2026-126365?
astro: before 7.4.3. prism: before 4.1.2. markdoc: from 0.3.0 before 2.1.2.Source: cve.now feed data
How do I fix CVE-2026-126365?
Upgrade to a fixed version: astro 7.4.3 · prism 4.1.2 · markdoc 2.1.2.Source: cve.now feed data