CVE-2023-36459

Mastodon vulnerable to Cross-site Scripting through oEmbed preview cards

MEDIUM

6.1

CVSS Score

Published: July 6, 2023 at 06:29 PM UTC

Updated: June 17, 2026 at 06:06 AM UTC

2 products affected across 2 vendorsMastodonMastodon

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Severity

MEDIUM6.1

Exploit prediction

EPSS 1%

SSVC

No known exploit

Description

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.

Affected

Our own answer: ranges merged, affected separated from platform-only, with confidence and review flags.

Mastodon · Joinmastodon

95%

1.3 ≤ v < 3.5.94.0.0 ≤ v < 4.0.54.1.0 ≤ v < 4.1.3

Affected range stops below 3.5.9, so it looks safe — our inference, not a vendor statement

Affected range stops below 4.0.5, so it looks safe — our inference, not a vendor statement

Affected range stops below 4.1.3, so it looks safe — our inference, not a vendor statement

Mastodon · Mastodon

60%

v < 3.5.9v < 4.0.5v < 4.1.3

Affected range stops below 3.5.9, so it looks safe — our inference, not a vendor statement

Affected range stops below 4.0.5, so it looks safe — our inference, not a vendor statement

Affected range stops below 4.1.3, so it looks safe — our inference, not a vendor statement

Remediation

No guide yet

No remediation guidance has been written for this CVE yet. What the record does show:

Patch and advisory references

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

References (6)

Mailing List

Source: [email protected]

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

x_refsource_MISCPatchThird Party Advisory

Source: [email protected]

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

x_refsource_MISCThird Party Advisory

Source: [email protected]

https://github.com/mastodon/mastodon/releases/tag/v3.5.9

x_refsource_MISCThird Party Advisory

Source: [email protected]

https://github.com/mastodon/mastodon/releases/tag/v4.0.5

x_refsource_MISCThird Party Advisory

Source: [email protected]

https://github.com/mastodon/mastodon/releases/tag/v4.1.3

x_refsource_CONFIRMThird Party Advisory

Source: [email protected]

https://github.com/mastodon/mastodon/security/advisories/GHSA-ccm4-vgcc-73hp

SSVC — Action Prioritization

SSVCNo known exploitNot automatableTotal impact

SSVC signals action urgency (what to patch first), separate from CVSS which measures severity.

CVSS

6.1MEDIUM[email protected]

Attack Vector: NETWORK
Complexity: LOW
Privileges: NONE
User Interaction: REQUIRED
Scope: CHANGED
Confidentiality: LOW
Integrity: LOW
Availability: NONE

Vector?

Quick Info

StatusMODIFIED

CWE

CWE-79

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