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EUVD-2026-333959

fkie_cve-2026-58657

Grav before 2.0.0 (affected through 2.0.0-rc.9 and the 2.0 branch) contains a stored CSS injection vulnerability in the Markdown image resize() media action. Prior media hardening rejects direct ?style= payloads and unsafe attribute() fallbacks, but the resize() action in Excerpts::processMediaActions() writes caller-controlled values directly into the image's styleAttributes. A lower-privileged content editor who can edit page Markdown can store a crafted image URL with semicolon-delimited CSS declarations in the resize parameters, which are rendered into the final <img style=...> attribute when a higher-privileged reviewer/admin views the page or preview. This does not require JavaScript execution but enables UI redress/overlay and content-manipulation attacks (e.g., a full-viewport fixed overlay). Fixed in 2.0.0.

GHSA-ffmg-hfvg-jhg9 — Grav: Stored CSS injection via Markdown image resize() bypasses prior media style sanitizers in Grav

Affected: Packagist: getgrav/grav

## Summary

Grav 2.0.0-rc.9 and the current 2.0 branch still allow stored CSS injection through Markdown image media actions. The prior media hardening rejects direct `?style=` payloads and unsafe `attribute()` fallbacks, but the adjacent `resize()` action still writes caller-controlled values directly into `styleAttributes`.

A publisher who can edit page Markdown can store a crafted image URL that renders additional CSS declarations in the final `<img style=...>` attribute. This crosses the same lower-privileged publisher to higher-privileged reviewer/admin rendered-content boundary as the earlier media style and attribute advisories.

## Impact

A lower-privileged content editor can persist CSS declarations that are rendered when a higher-privileged user views the page or admin preview. The demonstrated payload creates a full-viewport fixed overlay by injecting `position:fixed`, viewport dimensions, background color, and z-index declarations.

This does not require JavaScript execution. The impact is stored CSS injection in rendered content, with UI redress/overlay and content-manipulation risk in higher-privileged sessions.

## Reproduction

Tested versions:

- Grav 2.0 branch commit `6582166173bb8eb5869d96aea384e0e73777c94c` - Grav `2.0.0-rc.9` commit `e03d29aa0d3ece16d73c1ffccfa78df8bf5f28b8`

Minimal Markdown payload:

```markdown ![logo](image.png?resize=100;position:fixed;top:0;left:0;width:100vw;height:100vh;background:white;z-index:9999,200) ```

A minimal PHPUnit…