CVE-2023-42450

SSRF in Joinmastodon Mastodon 4.2.0

SSRF

Published

19 September 2023

Modified

21 November 2024

Patch / advisory

View advisory

CVSS Score v3.1 5.4

Click a component to see what it means

Raw vector

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:L/I:L/A:N

EPSS Score 0.0046 38th percentile

Risk Priority 42 floored blend · peak EPSS

CVSS and EPSS are reproduced from their sources (NVD, FIRST EPSS). Risk Priority is our own derived reading, not an NVD score.

Summary

CVE-2023-42450 is a medium-severity HTTP Request/Response Splitting (CWE-113) vulnerability in Joinmastodon Mastodon. Its CVSS base score is 5.4 (Medium).

Operationally, exploitation aligns with the MITRE ATT&CK technique Protocol or Service Impersonation (T1001.003); ranked at the 38th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.

OWASP Top 10 for Web (2025)

EU & UK References

🇪🇺 ENISA EUVD: EUVD-2023-46896

Vulnerability Data

Mastodon is a free, open-source social network server based on ActivityPub. Starting in version 4.2.0-beta1 and prior to version 4.2.0-rc2, by crafting specific input, attackers can inject arbitrary data into HTTP requests issued by Mastodon. This can be used to…

perform confused deputy attacks if the server configuration includes `ALLOWED_PRIVATE_ADDRESSES` to allow access to local exploitable services. Version 4.2.0-rc2 has a patch for the issue.

CWE(s): CWE-113 CWE-918

Related Threats

MITRE ATT&CK Enterprise Techniques

T1001.003 Protocol or Service Impersonation Command And Control

Adversaries may impersonate legitimate protocols or web service traffic to disguise command and control activity and thwart analysis efforts.

attack.mitre.org →

T1003.001 LSASS Memory Credential Access

Adversaries may attempt to access credential material stored in the process memory of the Local Security Authority Subsystem Service (LSASS).

attack.mitre.org →

T1003.005 Cached Domain Credentials Credential Access

Adversaries may attempt to access cached domain credentials used to allow authentication to occur in the event a domain controller is unavailable.

attack.mitre.org →

T1003.007 Proc Filesystem Credential Access

Adversaries may gather credentials from the proc filesystem or `/proc`.

attack.mitre.org →

T1006 Direct Volume Access Stealth

Adversaries may directly access a volume to bypass file access controls and file system monitoring.

attack.mitre.org →

T1018 Remote System Discovery Discovery

Adversaries may attempt to get a listing of other systems by IP address, hostname, or other logical identifier on a network that may be used for Lateral Movement from the current system.

attack.mitre.org →

Derived from this CVE’s CWE(s) via the direct CWE→ATT&CK cross-walk.

CVEs Like This One

CVE-2026-27477Same product: Joinmastodon Mastodon

CVE-2026-22245Same product: Joinmastodon Mastodon

CVE-2025-62175Same product: Joinmastodon Mastodon

CVE-2023-36461Same product: Joinmastodon Mastodon

CVE-2025-27157Same product: Joinmastodon Mastodon

CVE-2026-23963Same product: Joinmastodon Mastodon

CVE-2026-23962Same product: Joinmastodon Mastodon

CVE-2025-54879Same product: Joinmastodon Mastodon

CVE-2023-36460Same product: Joinmastodon Mastodon

CVE-2025-62174Same product: Joinmastodon Mastodon

Affected Assets

joinmastodon

mastodon

4.2.0

Mitigating Controls

Control response

Prevent

Stop it (NIST 800-53)

—

Detect

Catch it (NIST detect / respond)

—

Harden

Shrink the surface (DISA STIG)

—

Validate

Prove the fix (OWASP ASVS)

V3.4.2
V4.1.3
V1.3.6
V4.2.3

Likely Mitigating Controls AI

Per-CVE control mapping for this CVE has not run yet; the list below is derived from the weakness types (CWEs) cited in the NVD entry.

CA-8 Penetration Testing

addresses: CWE-918

Penetration testing attempts server-side requests to internal resources, identifying SSRF weaknesses for remediation.

SC-7 Boundary Protection

addresses: CWE-918

Outbound connections to external resources can be monitored and limited at the boundary, reducing SSRF impact.

SI-10 Information Input Validation

addresses: CWE-918

Validates server-side URLs and resource references to block SSRF attempts.

SI-4 System Monitoring

addresses: CWE-918

Detects server-side request forgery through monitoring of unexpected outbound connections.

Mitigating Controls (NIST CSF 2.0) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.

DE.CM-09 partial match

blocks

Runtime monitoring of web applications and services can detect anomalous outbound requests indicative of SSRF.

ID.RA-01 partial match

blocks

Vulnerability identification processes can discover and record SSRF flaws in web applications.

PR.IR-01 partial match

blocks

Network segmentation and egress controls can limit the damage from successful SSRF requests.

PR.PS-06 partial match

blocks

Secure SDLC practices directly require input sanitization and header handling that prevent CRLF injection.

Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.

A.5.1 Policies for information security partial match

removes

A.5.14 Information transfer partial match

removes

A.5.15 Access control partial match

removes

A.5.16 Identity management partial match

removes

A.5.17 Authentication information partial match

removes

A.5.18 Access rights partial match

removes