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CVE-2026-8630· NVD / CVE Program· CNA VulnCheck

justhtml before 1.12.0 Mutation XSS via Raw Text Elements

justhtml before 1.12.0 (versions <= 1.11.0) contains a mutation cross-site scripting (mXSS) vulnerability in the serialization of raw-text elements such as <style> and <script>. When a DOM tree is processed by sanitize_dom() using a custom policy that keeps these elements, text nodes inside them are serialized literally without escaping, allowing attacker-controlled text containing the matching closing tag sequence to break out of the raw-text context and inject arbitrary HTML into the serialized output. The default sanitization policy is not affected because it drops the contents of style and script.

MediumCVSS 5.1 · v4.0—No exploit Fix available
Published
Aug 23, 2026
Updated
Aug 26, 2026
EPSS
0.3% · 16th percentile
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Report tools

JSON

Action score

20

Monitor

Low priority for now.

CVSS
20 / 40 · 5.1 / 10
CISA KEV
0 / 30 · Not listed
EPSS
0 / 30 · 0.3%

CISA SSVC decision

Exploitation
none
Automatable
no
Technical impact
partial

Vulnrichment: CISA's decision-tree inputs.

CNA vs NVD score

NVD
—
CNA · VulnCheck
5.1
NVD has not scored this yet; the score shown is the CNA’s.

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:A/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N

The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.

Noroxi analysis

No Noroxi analysis for this record yet

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Affected systems

—

Versions reported by the vendor

Affected version ranges reported by the assigning authority (VulnCheck). Independent of NVD's CPE analysis and usually ahead of it.

  • EmilStenstrom justhtml

    • 1.12.0not affected
    • before 1.12.0affected · semver

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

EcosystemPackageAffected rangeFix
PyPIjusthtmlbefore 1.12.01.12.0

Same product

emilstenstrom: all records

Other highest-scoring records for the same primary product.

  • CVE-2026-8445justhtml before 1.12.0 Sanitizer Bypass via Markdown
    37Monitor
  • CVE-2026-7808justhtml before 1.16.0 Multiple Security Issues via Sanitization
    37Monitor
  • CVE-2026-5388justhtml before 1.15.0 Multiple Security Issues
    37Monitor
  • CVE-2026-9769justhtml before 1.10.0 Denial of Service via deeply nested HTML
    34Monitor
  • CVE-2026-4671justhtml before 1.18.0 Denial of Service via CSS Selector
    34Monitor
  • CVE-2026-77088justhtml 0.9.0 through 1.21.0 Cross-Site Scripting via code-span
    21Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / packageFixed versionSource
EmilStenstrom justhtml1.12.0Vendor (CNA)
PyPI:justhtml1.12.0Package registry (OSV)

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

No dated events beyond publication.

EPSS, last 120 days

FIRST EPSS daily score; only changes of 0.01 or more are recorded (step chart).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

No commit or PR link among the references.

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

  • CVE-2026-84450 days apartjusthtml before 1.12.0 Sanitizer Bypass via Markdown
    37Monitor
  • CVE-2026-770880 days apartjusthtml 0.9.0 through 1.21.0 Cross-Site Scripting via code-span
    21Monitor
  • CVE-2026-57510 days apartjusthtml before 1.14.0 Mutation XSS via custom sanitization policies
    20Monitor
  • CVE-2026-68270 days apartjusthtml before 1.17.0 Multiple Cross-Site Scripting Vulnerabilities
    20Monitor
  • CVE-2026-747930 days apartjusthtml before 3.11.0 XSS via selectedcontent projection
    20Monitor

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

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Bug bounty scope

No known public program.

Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).

Technical details

Attack conditions

  • Anyone who can reach it over the internet can trigger it.
  • No account or password is required.
  • No special conditions are required; it is repeatable.

If successful

Confidentiality
Integrity
Availability
Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
A
Scope
X

Weakness class (CWE)

CWE-79 · Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')

CVSS vector

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:A/VC:N/VI:N/VA:N/SC:L/SI:L/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

nvd-secondary

Root cause

User content is inserted into the page as HTML. The browser interprets the content as code rather than data.

The bug in code

The whole CWE-79 class

A representative example of this vulnerability class. Not the vendor's source code; it shows the faulty pattern and its fix.

Vulnerable

ts
commentEl.innerHTML = comment.body;

Fixed

ts
commentEl.textContent = comment.body;

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

ATT&CK techniques

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Change log

  1. Fix✗ → ✓

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References

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records