TI-2023-18300 Aliases CVE-2023-36459

Mastodon vulnerable to Cross-site Scripting through oEmbed preview cards

MEDIUM 44CWE-79Published 2023-07-06 · Updated 2025-02-13

Key facts

Attack vector: Network
Privileges required: None
User interaction: Required
Attack complexity: Low
Impact type: Cross-site scripting
Confidentiality · integrity · availability: High · High · None
Fix status: Fixed

Attack profile from CVSS 3.1 · CNA. Fix status from CNA. Impact type from CWE-79.

Summary

Mastodon is a free, open-source social network server based on ActivityPub. Starting in version 1.3 and prior to versions 3.5.9, 4.0.5, and 4.1.3, an attacker using carefully crafted oEmbed data can bypass the HTML sanitization performed by Mastodon and include arbitrary HTML in oEmbed preview cards. This introduces a vector for cross-site scripting (XSS) payloads that can be rendered in the user's browser when a preview card for a malicious link is clicked through. Versions 3.5.9, 4.0.5, and 4.1.3 contain a patch for this issue.

Why it matters now

Exploitation None reported CISA SSVC · not in CISA KEV

EPSS 0.01217 68th percentileScored 2026-11-07

Fix Fixed mastodon (mastodon): 3.5.9, 4.0.5, 4.1.3

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation: None
Automatable: No
Technical impact: Total

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

Vendor	Product	Affected versions	Fixed in	Status	Source
mastodon	mastodon	1.3 to before 3.5.9; 4.0.0 to before 4.0.5; 4.1.0 to before 4.1.3	3.5.9, 4.0.5, 4.1.3	Patch available	CNA

mastodon Vendormastodon Affected 1.3 to before 3.5.9; 4.0.0 to before 4.0.5; 4.1.0 to before 4.1.3 Fixed in 3.5.9, 4.0.5, 4.1.3 Patch available CNA

CPE configurations NVD · 1

CPE	Versions	Role	Vendor
cpe:2.3:a:joinmastodon:mastodon::::::::	1.3 to before 3.5.9; 4.0.0 to before 4.0.5; 4.1.0 to before 4.1.3	Vulnerable	mastodon

cpe:2.3:a:joinmastodon:mastodon:*:*:*:*:*:*:*:* Versions 1.3 to before 3.5.9; 4.0.0 to before 4.0.5; 4.1.0 to before 4.1.3 Vulnerable ·mastodon

Remediation

Fix · CNA mastodon (mastodon) Fixed in 3.5.9, 4.0.5, 4.1.3

Timeline

2026-10-02 Threatist record created from CVE-2023-36459

References

Patch 1

https://github.com/mastodon/mastodon/commit/6d8e0fae3e96f3cf4febe03fa7fcf5b95ff761b2

Advisory 4

Other 1

http://www.openwall.com/lists/oss-security/2023/07/06/5

TI-2022-02004 Improper Restriction of Excessive Authentication Attempts in mastodon/mastodon CVSS 3.1CRITICAL 9.8
TI-2025-34613 Mastodon e‑mail throttle misconfiguration allows unlimited email confirmations against unconfirmed emails CVSS 3.1HIGH 7.5
TI-2022-22936 Mastodon through 4.0.2 allows attackers to cause a denial of service (large Sidekiq pull… CVSS 3.1HIGH 7.5
TI-2023-18301 Mastodon vulnerable to arbitrary file creation through media attachments CVSS 3.1CRITICAL 10.0
TI-2023-13359 Mastodon's blind LDAP injection in login allows the attacker to leak arbitrary attributes from LDAP database CVSS 3.1HIGH 7.7
TI-2024-16846 External OpenID Connect Account Takeover by E-Mail Change in mastodon CVSS 3.1HIGH 7.4

See all 41 →

Sources

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