CVE-2023-36459Network attack vector

Cross-site scripting via unsanitized oEmbed HTML

Published Jul 6, 2023 · Updated Feb 13, 2025

Cross-site scripting in Mastodon 1.3 through 3.5.8, 4.0.0 through 4.0.4, and 4.1.0 through 4.1.2 allows remote attackers to run script. The preview-card serializer returned stored object.html without render-time sanitization, while MASTODON_OEMBED inherited the broader RELAXED allowlist. Exploitation requires a user to click through a malicious link's preview card, after which the payload runs in that user's browser.

CVSS severity9.3
Critical
EPSS probability1.22%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Book a demo

Summary

What happened

Cross-site scripting in Mastodon 1.3 through 3.5.8, 4.0.0 through 4.0.4, and 4.1.0 through 4.1.2 allows remote attackers to run script. The preview-card serializer returned stored object.html without render-time sanitization, while MASTODON_OEMBED inherited the broader RELAXED allowlist. Exploitation requires a user to click through a malicious link's preview card, after which the payload runs in that user's browser.

The record

CVE
CVE-2023-36459
Published
Jul 6, 2023
Updated
Feb 13, 2025
Vendor
Mastodon
Product
Mastodon
Classifications
CWE-79, T1059.007
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jul 6, 2023CVE publishedPublication date reported by the CVE source.
  2. Feb 13, 2025Record 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?

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

  1. Affected versionversion=>= 1.3, < 3.5.9
  2. Affected versionversion=>= 4.0.0, < 4.0.5
  3. Affected versionversion=>= 4.1.0, < 4.1.3

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Mastodon · Mastodonversion=>= 1.3, < 3.5.9; version=>= 4.0.0, < 4.0.5; version=>= 4.1.0, < 4.1.3

Published CVSS scores

9.3GitHubCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/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 exploitUnconfirmed

Weakness, pattern, technique

CWE-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
T1059.007Command and Scripting Interpreter: JavaScript

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

See the directory against your own environment.

Your stack

Check the software in your environment

Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.

Book a demo