Impact

The HTML backend did not perform sufficient validation during resource handling:

• Accepted file:// URIs enabling local file system access when enable_local_fetch=True
• Path resolution allowed traversal outside intended directories via ../ sequences and absolute paths
• Did not block internal network resources under enable_remote_fetch=True
• HTTP redirects were not validated, potentially redirecting to unintended schemes
• No resource limits for remote image downloads and data: URIs

Patches

Fixed in versions 2.91.0 (initial fixes) and 2.94.0 (additional improvements). The fixes implement:

• Updated local path treatment: absolute files always blocked, relative paths require enable_local_fetch=True (default: False) and containment within configured base_path for path traversal protection
• file:// scheme stripped & treated as local path (above)
• IP address validation to prevent SSRF
• HTTP redirect validation, connection and read timeouts
• Size limit for both remote images (with streaming download) and base64-decoded data URIs

Workarounds

Keep both enable_local_fetch=False and enable_remote_fetch=False (defaults) when processing untrusted HTML documents.

References

• Initial fixes: v2.91.0
• Additional improvements: v2.94.0