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posted by janrinok on Saturday May 05 2018, @01:51AM   Printer-friendly
from the not-the-best-best-explanation dept.

Submitted via IRC for SoyCow8317

NT LAN Manager (NTLM) credentials can be stolen via malicious Portable Document Format (PDF) files without user interaction.

PDF files, the security researchers explain, consist primarily of objects, together with Document structure, File structure, and content streams. There are eight basic types of objects, including dictionaries, and a malicious actor can abuse these to steal NTLM credentials.

A dictionary object represents a table containing pairs of objects, called entries, where the first element is the key (a name) and the second element is the value (may be any kind of object). Represented by dictionary objects, the pages of a document are called page objects and consist of required and optional entries.

One of the optional entries is the /AA entry, defining actions performed when a page is opened (/O entry) or closed (/C entry). An action dictionary is held within /O (/C) and consists of 3 required entries: /S, /F, and /D, describing the type of action to be performed – GoToR (Go To Remote) and GoToE (Go To Embedded) –, the location location [sic] of the other PDF, and the location to go to within the document.

"By injecting a malicious entry (using the fields described above together with his SMB server details via the '/F' key), an attacker can entice arbitrary targets to open the crafted PDF file which then automatically leaks their NTLM hash, challenge, user, host name and domain details," Check Point explains.

Source: https://www.securityweek.com/pdf-files-can-silently-leak-ntlm-credentials


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  • (Score: 2, Informative) by Anonymous Coward on Saturday May 05 2018, @02:22AM (2 children)

    by Anonymous Coward on Saturday May 05 2018, @02:22AM (#675947)

    Found this MS security article [microsoft.com] stating (emphasis mine):

    Microsoft is releasing an optional security enhancement to NT LAN Manager (NTLM), limiting which network resources various clients in the Windows 10 or the Windows Server 2016 operating systems can use NTLM Single Sign On(SSO) as an authentication method. When you deploy the new security enhancement with a Network Isolation Policy defining your organization's resources, attackers can no longer redirect a user to a malicious resource outside your organization to obtain the NTLM authentication messages. This new behavior is optional, and requires customers who wish to enable it to opt in via a Windows Registry Setting or other means described below.

    So Adobe is leaving this security vulnerability in place because of an obscure MS option to prevent it.

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  • (Score: 3, Insightful) by Gaaark on Saturday May 05 2018, @02:57AM (1 child)

    by Gaaark (41) on Saturday May 05 2018, @02:57AM (#675951) Journal

    And that obscure option is open it in Linux?

    ;)

    --
    --- Please remind me if I haven't been civil to you: I'm channeling MDC. ---Gaaark 2.0 ---
    • (Score: 0) by Anonymous Coward on Saturday May 05 2018, @03:16AM

      by Anonymous Coward on Saturday May 05 2018, @03:16AM (#675958)

      Linux don't play dat game