Dark Reading is part of the Informa Tech Division of Informa PLC

This site is operated by a business or businesses owned by Informa PLC and all copyright resides with them.Informa PLC's registered office is 5 Howick Place, London SW1P 1WG. Registered in England and Wales. Number 8860726.

Endpoint Security //

Identity Management

3/1/2019
07:00 AM
Larry Loeb
Larry Loeb
Larry Loeb
50%
50%

Digital Signatures Can Be Forged in PDF Docs

Researchers in Germany have figured out three different ways to forge digital signatures in PDF documents.

Researchers at the Ruhr-University Bochum in Germany have figured out three different ways to forge digital signatures in PDF documents.

The fakes will be treated as genuine on 21 of 22 desktop PDF viewer apps (running on Windows, MacOS and Linux) and five out of seven online PDF digital signing services. These include well-known apps, including Adobe Acrobat Reader, Foxit Reader and LibreOffice, as well as online services like DocuSign and Evotrust.

Summarizing their six month-long research in a paper and a blog, the researchers note they have been working with Germany's Computer Emergency Response Team (BSI-CERT) to responsibly disclose the results to affected service providers.

Signatures to PDF documents have come to be accepted in legally binding contracts since President Clinton signed the eSign Act. In 2014, the EU issued a regulation that gave such documents legal status in the EU as well.

Adobe has said that it processed 8 billion such signatures in 2017. The researchers found three major attack methods.

The first is Universal Signature Forgery (USF). This is a way for attackers to game the signature verification process so that it will display a fake panel/message that the signature is valid.

The second is Incremental Saving Attack (ISA). Here, attackers will add content to an already signed PDF document via the "incremental saving (incremental update)" mechanism, but without breaking what has already been saved for the signature of that document.

The last is Signature Wrapping (SWA). Similar to ISA, it will fool the signature validation process into "wrapping" around the attacker's additional content. This means the content added (the incremental update) has been digitally signed.

The researchers found that there were two root causes why this sort of spoofing could be carried out.

First, they said, "The specification does not provide any information with concrete procedure on how to validate signatures. There is no description of pitfalls and any security considerations. Thus, developers must implement the validation on their own without a best-common-practice information."

Secondly, they found "The error tolerance of the PDF viewer is abused to create non-valid documents bypassing the validation, yet correctly displayed to the user."

They came up with a verification algorithm. It's a concrete approach on how to compute the values necessary for the verification and how to detect manipulations after signing the PDF file. The specified algorithm must be applied for each signature within the PDF document. As an input, it requires the PDF file as a byte stream and the signature object.

The approach will only work on the last revision that has been done to a PDF document, and does not verify any signatures that may have been done previously to that final revision.

This problem can be serious, and enable some massive financial frauds. It is incumbent on the security team to verify that they have patched all applications affected, and that they are using services that have taken this problem seriously.

— Larry Loeb has written for many of the last century's major "dead tree" computer magazines, having been, among other things, a consulting editor for BYTE magazine and senior editor for the launch of WebWeek.

Comment  | 
Print  | 
More Insights
Comments
Newest First  |  Oldest First  |  Threaded View
COVID-19: Latest Security News & Commentary
Dark Reading Staff 7/9/2020
Omdia Research Launches Page on Dark Reading
Tim Wilson, Editor in Chief, Dark Reading 7/9/2020
Mobile App Fraud Jumped in Q1 as Attackers Pivot from Browsers
Jai Vijayan, Contributing Writer,  7/10/2020
Register for Dark Reading Newsletters
White Papers
Video
Cartoon
Current Issue
Special Report: Computing's New Normal, a Dark Reading Perspective
This special report examines how IT security organizations have adapted to the "new normal" of computing and what the long-term effects will be. Read it and get a unique set of perspectives on issues ranging from new threats & vulnerabilities as a result of remote working to how enterprise security strategy will be affected long term.
Flash Poll
The Threat from the Internetand What Your Organization Can Do About It
The Threat from the Internetand What Your Organization Can Do About It
This report describes some of the latest attacks and threats emanating from the Internet, as well as advice and tips on how your organization can mitigate those threats before they affect your business. Download it today!
Twitter Feed
Dark Reading - Bug Report
Bug Report
Enterprise Vulnerabilities
From DHS/US-CERT's National Vulnerability Database
CVE-2020-15105
PUBLISHED: 2020-07-10
Django Two-Factor Authentication before 1.12, stores the user's password in clear text in the user session (base64-encoded). The password is stored in the session when the user submits their username and password, and is removed once they complete authentication by entering a two-factor authenticati...
CVE-2020-11061
PUBLISHED: 2020-07-10
In Bareos Director less than or equal to 16.2.10, 17.2.9, 18.2.8, and 19.2.7, a heap overflow allows a malicious client to corrupt the director's memory via oversized digest strings sent during initialization of a verify job. Disabling verify jobs mitigates the problem. This issue is also patched in...
CVE-2020-4042
PUBLISHED: 2020-07-10
Bareos before version 19.2.8 and earlier allows a malicious client to communicate with the director without knowledge of the shared secret if the director allows client initiated connection and connects to the client itself. The malicious client can replay the Bareos director's cram-md5 challenge to...
CVE-2020-11081
PUBLISHED: 2020-07-10
osquery before version 4.4.0 enables a priviledge escalation vulnerability. If a Window system is configured with a PATH that contains a user-writable directory then a local user may write a zlib1.dll DLL, which osquery will attempt to load. Since osquery runs with elevated privileges this enables l...
CVE-2020-6114
PUBLISHED: 2020-07-10
An exploitable SQL injection vulnerability exists in the Admin Reports functionality of Glacies IceHRM v26.6.0.OS (Commit bb274de1751ffb9d09482fd2538f9950a94c510a) . A specially crafted HTTP request can cause SQL injection. An attacker can make an authenticated HTTP request to trigger this vulnerabi...