What is CVE-2026-28509?

CVE-2026-28509 is a medium-severity vulnerability in Langbot, classified under Cross-site Scripting. CVSS score: 6.3/10. Published 2026-03-06.

How severe is CVE-2026-28509?

Medium severity. CVSS v3 base score is 6.3 out of 10.

XSS in Langbot

CVE-2026-28509

LangBot is a global IM bot platform designed for LLMs. Prior to version 4.8.7, LangBot’s web UI renders user-supplied raw HTML using rehypeRaw, which can lead to a cross-site scripting (XSS) vulnerability. This issue has been patched in version 4.8.7.

Vulnerability class: XSS (Cross-Site Scripting)

EPSS: 0.002 (8.6th percentile) — read the EPSS interpretation.

CVSS v3 metric

CVSS v3 base score 6.3 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:H/I:L/A:N.

Affected products

Langbot
Langbot-app Langbot — versions < 4.8.7

Weakness classification (CWE)

CWE-79 — Cross-site Scripting

References

security-advisories@github.com (x_refsource_CONFIRM, Exploit, Vendor Advisory)
security-advisories@github.com (Patch, x_refsource_MISC)

Frequently asked questions

What is CVE-2026-28509?: CVE-2026-28509 is a medium-severity vulnerability in Langbot, classified under Cross-site Scripting. CVSS score: 6.3/10. Published 2026-03-06.
How severe is CVE-2026-28509?: Medium severity. CVSS v3 base score is 6.3 out of 10.