CVE-2026-27570Network attack vector

Stored XSS via unescaped shared conversation title

Published Mar 19, 2026 · Updated Mar 19, 2026

Stored XSS in Discourse before 2026.3.0-latest.1, 2026.2.1, and 2026.1.2 allows remote authenticated users to run scripts in viewers' browsers. SharedAiConversation#onebox interpolates the unescaped conversation title into an HTML anchor, preserving attacker-supplied tags and script. Exploitation requires low-privileged access to create a shared AI conversation and passive interaction by a user who views its onebox preview, exposing browser-accessible data and actions.

CVSS severity5.1
Medium
EPSS probability0.35%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Stored XSS in Discourse before 2026.3.0-latest.1, 2026.2.1, and 2026.1.2 allows remote authenticated users to run scripts in viewers' browsers. SharedAiConversation#onebox interpolates the unescaped conversation title into an HTML anchor, preserving attacker-supplied tags and script. Exploitation requires low-privileged access to create a shared AI conversation and passive interaction by a user who views its onebox preview, exposing browser-accessible data and actions.

The record

CVE
CVE-2026-27570
Published
Mar 19, 2026
Updated
Mar 19, 2026
Vendor
Discourse
Product
Discourse
Classifications
CWE-79, T1203
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Mar 19, 2026CVE publishedPublication date reported by the CVE source.
  2. Mar 19, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=>= 2026.1.0-latest, < 2026.1.2
  2. Affected versionversion=>= 2026.2.0-latest, < 2026.2.1
  3. Affected versionversion== 2026.3.0-latest

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Discourse · Discourseversion=>= 2026.1.0-latest, < 2026.1.2; version=>= 2026.2.0-latest, < 2026.2.1; version== 2026.3.0-latest

Published CVSS scores

5.1GitHub, Inc.CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:P/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N
6.1NIST NVDCVSS: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 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

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

Public exploit references

No public exploit references are available in this record.

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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