CVE-2026-77088Public exploitNetwork attack vector

Cross-site scripting via blank-line code-span breakout

Published Aug 23, 2026 · Updated Aug 23, 2026

Cross-site scripting in JustHTML 0.9.0 through 1.21.0 allows remote attackers to execute script via crafted code or pre text. The to_markdown() path sends verbatim code and linked pre text with blank lines to _markdown_code_span(), which sizes only the backtick fence and emits later text unescaped. Exploitation requires attacker-controlled HTML to pass through default sanitization and Markdown conversion, followed by a user viewing the output in a compliant renderer that permits raw HTML.

CVSS severity5.3
Medium
EPSS probability0.19%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Cross-site scripting in JustHTML 0.9.0 through 1.21.0 allows remote attackers to execute script via crafted code or pre text. The to_markdown() path sends verbatim code and linked pre text with blank lines to _markdown_code_span(), which sizes only the backtick fence and emits later text unescaped. Exploitation requires attacker-controlled HTML to pass through default sanitization and Markdown conversion, followed by a user viewing the output in a compliant renderer that permits raw HTML.

The record

CVE
CVE-2026-77088
Published
Aug 23, 2026
Updated
Aug 23, 2026
Vendor
Emil Stenström
Product
JustHTML
Classifications
CWE-79, CWE-116, T1203
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 23, 2026CVE publishedPublication date reported by the CVE source.
  2. Aug 23, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Affected versions are unavailable in this record. Check the vendor advisory for version and patch details.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Emil Stenström · JustHTMLAffected versions are unavailable in this record.

Published CVSS scores

5.3VulnCheckCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:L/VI:L/VA:N/SC:L/SI:L/SA:N
6.1VulnCheckCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
CWE-116Improper Encoding or Escaping of Output
T1203Exploitation for Client Execution

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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