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12/07/2026 12:19 pm
TL;DR: Malicious PDFs can trigger code execution through reader flaws, embedded JavaScript, XFA forms, or remote actions that force network callbacks and credential leakage, according to SentinelOne. The practical issue is not the file type itself but the trust assumptions built into PDF handling, browser rendering, and Windows authentication flows.
NHIMG editorial — based on content published by SentinelOne: malicious PDF files, code execution, and credential leakage
Questions worth separating out
Q: What breaks when PDF readers are allowed to execute active content by default?
A: Default active-content handling turns a document viewer into a runtime execution surface.
Q: Why do malicious PDFs create identity risk as well as endpoint risk?
A: Because a crafted PDF can force a callback that exposes NTLM material or other authentication data without explicit user intent.
Q: How do security teams reduce callback abuse from PDF files?
A: They should disable unnecessary PDF scripting, block remote document actions, and prevent untrusted outbound connections from reader processes.
Practitioner guidance
- Disable unnecessary PDF JavaScript Turn off Acrobat JavaScript and equivalent active-content features wherever the business does not need interactive PDFs.
- Block untrusted remote PDF actions Restrict GoToR-style actions and outbound SMB connections from PDF readers so a document cannot force credential-bearing network calls to attacker-controlled infrastructure.
- Harden NTLM exposure on managed endpoints Review whether systems still auto-negotiate NTLM in places where Kerberos or other controlled authentication paths are available.
What's in the full article
SentinelOne's full article covers the technical parsing details this post intentionally leaves for the source:
- Byte-level walkthrough of PDF object structure, streams, dictionaries, and encoded JavaScript
- Examples of compressed and octal-encoded payloads that reveal how malicious content hides in plain sight
- Reader-side mitigation options such as Acrobat JavaScript controls and Windows NTLM handling
- Discussion of EDR visibility, firewall controls, and file-scanning approaches for enterprise environments
👉 Read SentinelOne's technical walkthrough of malicious PDF execution paths →
Malicious PDFs and NTLM leakage: what should defenders change?
Explore further
12/07/2026 12:33 pm
Malicious PDFs are really a control-gap problem, not just a file-format problem. The article shows that execution can come from reader flaws, active content, or remote references, which means the defensive question is where rendering is allowed and what it can reach. Once a document can cause outbound authentication or script execution, the boundary between content handling and identity exposure collapses. Practitioners should treat PDF processing as a governed execution surface, not a harmless viewer task.
A question worth separating out:
Q: What should organisations review first after a PDF credential-leak alert?
A: Start with the endpoint, the reader configuration, and the authentication path that was exposed. Confirm whether the callback used NTLM, whether the destination was approved, and whether similar document actions are allowed elsewhere in the estate. The immediate goal is containment of the exposure path, then policy correction across all managed PDF viewers.
👉 Read our full editorial: Malicious PDFs exploit reader flaws, JavaScript, and NTLM leakage
