Raw vector
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:NCVSS and EPSS are reproduced from their sources (NVD, FIRST EPSS). Risk Priority is our own derived reading, not an NVD score.
Summary
CVE-2025-1521 is a medium-severity SSRF (CWE-918) vulnerability in Posthog Posthog. Its CVSS base score is 6.5 (Medium).
Operationally, ranked in the top 49% of CVEs by exploit likelihood; it is not currently listed in the CISA KEV catalog.
The strongest mitigations our analysis identified map to AC-4 (Information Flow Enforcement) and SI-10 (Information Input Validation) — see the control section below for these in your framework.
Deeper analysis AI-assisted summary
Synthesised by an AI model from the NVD description and linked references — a reading aid, not an authoritative source.
CVE-2025-1521 is a server-side request forgery vulnerability affecting the slack_incoming_webhook parameter handling in PostHog. The flaw stems from insufficient validation of supplied URIs before the application retrieves remote resources, enabling information disclosure on affected installations. It was originally reported as ZDI-CAN-25352 and carries a CVSS 3.1 base score of 6.5.
Authenticated remote attackers can supply a crafted webhook URI to induce the PostHog service account to access arbitrary internal or external resources, resulting in the exposure of sensitive information. The vulnerability requires valid credentials but no user interaction, and the CVSS vector reflects network-accessible exploitation with high confidentiality impact.
A fix was implemented in the PostHog repository via commit 6e8f035f9acd339c5ba87ba6ea40fc1ab3053d42, and the issue is detailed in Zero Day Initiative advisory ZDI-25-096.
The EPSS score rose from a low baseline to a recorded peak of 0.0121, indicating emerging exploitation interest after public disclosure.
OWASP Top 10 for Web (2025)
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2025-12185
Vulnerability Data
PostHog slack_incoming_webhook Server-Side Request Forgery Information Disclosure Vulnerability. This vulnerability allows remote attackers to disclose sensitive information on affected installations of PostHog. Authentication is required to exploit this vulnerability. The specific flaw exists within the processing of the slack_incoming_webhook parameter.…
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The issue results from the lack of proper validation of a URI prior to accessing resources. An attacker can leverage this vulnerability to execute code in the context of the service account. Was ZDI-CAN-25352.
- CWE(s)
Related Threats
CVEs Like This One
Affected Assets
Mitigating Controls
Control response
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Mitigating Controls (NIST 800-53 r5) AI
Information flow enforcement can restrict which destinations the server is allowed to contact on behalf of users.
Input validation directly stops untrusted URLs from being accepted and fetched without destination checks.
Boundary protection limits the network reach of server-initiated requests even if SSRF occurs.
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.
Secure development practices directly include input validation and destination allow-listing that prevent SSRF.
Runtime monitoring of web applications and services can detect anomalous outbound requests indicative of SSRF.
Vulnerability identification processes can discover and record SSRF flaws in web applications.
Network segmentation and egress controls can limit the damage from successful SSRF requests.