Unofficial 'patch' for Adobe Reader, Acrobat zero-day

In response to in-the-wild zero-day attacks targeting critical flaws in Adobe's Reader/Acrobat products, a respected security researcher is offering up a home-brewed (unofficial) patch for Windows users.The buyer-beware patch -- which is simply a replacement for the vulnerable AcroRd32.

In response to in-the-wild zero-day attacks targeting critical flaws in Adobe's Reader/Acrobat products, a respected security researcher is offering up a home-brewed (unofficial) patch for Windows users.

The buyer-beware patch -- which is simply a replacement for the vulnerable AcroRd32.dll -- is the handiwork of Lurene 'Pusscat' Grenier, a reverse-engineering guru attached to Sourcefire.  It's only available for Adobe Reader 9.0.  Here are the basic installation instructions:

  • Download this zip file.
  • Unzip it into C:\Program Files\Adobe\Reader 9.0\Reader\
  • Allow it to overwrite the old version.

According to Grenier, the patch should not be seen as a cure-all for the myriad of problems in Adobe's products.

"It may not prevent all attacks on jbig2 - it WILL prevent all current attacks using the method I described, but there may be others," she warned.

Grenier was the first to offer a detailed technical explanation of the underlying vulnerability.

If an unofficial patch is too much of a risk, Adobe Acrobat/Reader users should immediately follow the following advice from US-CERT:

Disable JavaScript in Adobe Reader and Acrobat

Disabling JavaScript may prevent some exploits from resulting in code execution. Acrobat JavaScript can be disabled using the Preferences menu (Edit -> Preferences -> JavaScript and un-check Enable Acrobat JavaScript).

Prevent Internet Explorer from automatically opening PDF documents

The installer for Adobe Reader and Acrobat configures Internet Explorer to automatically open PDF files without any user interaction. This behavior can be reverted to the safer option of prompting the user by importing the following as a .REG file:

Windows Registry Editor Version 5.00

[HKEY_CLASSES_ROOT\AcroExch.Document.7] "EditFlags"=hex:00,00,00,00

Disable the display of PDF documents in the web browser

Preventing PDF documents from opening inside a web browser will partially mitigate this vulnerability. If this workaround is applied it may also mitigate future vulnerabilities.

To prevent PDF documents from automatically being opened in a web browser, do the following:

1. Open Adobe Acrobat Reader. 2. Open the Edit menu. 3. Choose the preferences option. 4. Choose the Internet section. 5. Un-check the "Display PDF in browser" check box.

Do not access PDF documents from untrusted sources

Do not open unfamiliar or unexpected PDF documents, particularly those hosted on web sites or delivered as email attachments. Please see Cyber Security Tip ST04-010.