CVE-2026-77088 PUBLISHED

justhtml 0.9.0 through 1.21.0 Cross-Site Scripting via code-span

Assigner: VulnCheck
Reserved: 20.08.2026 Published: 23.08.2026 Updated: 23.08.2026

justhtml versions 0.9.0 through 1.21.0 contain a cross-site scripting vulnerability in to_markdown() where inline code spans fail to account for blank lines as block boundaries. Attackers can inject blank lines into code or pre element text to break the inline span, causing sanitized HTML to be emitted unescaped and re-parsed as live Markdown by compliant renderers.

CVSS Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:L/VI:L/VA:N/SC:L/SI:L/SA:N
CVSS Score: 5.3

Exploitability Metrics		Vulnerable System Impact Metrics		Subsequent System Impact Metrics
Attack Vector	Network	Confidentiality	Low	Confidentiality	Low
Attack Complexity	Low	Integrity	Low	Integrity	Low
Attack Requirements	None	Availability	None	Availability	None
Privileges Required	None
User Interaction	Passive

CVSS 4.0

CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
CVSS Score: 6.1

Attack Vector	Network	Scope	Changed
Attack Complexity	Low	Confidentiality Impact	Low
Privileges Required	None	Integrity Impact	Low
User Interaction	Required	Availability Impact	None

CVSS 3.1

Product Status

Vendor	EmilStenstrom
Product	justhtml
Versions	Default: affected unaffected from 0 to 0.9.0 (excl.)

Credits

seankohjs reporter
yueyueL reporter

References

Problem Types

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