CVE-2024-3900

What it actually does

Out-of-bounds array write during PDF ActualText Unicode sequence processing, resulting in memory corruption in the Xpdf parser.

Why it matters to the business

Low-risk denial of service when opening specially crafted PDF files on systems using Xpdf 4.05 or earlier; limited operational disruption due to high attack complexity and local attack vector.

How an attack unfolds

An attacker creates a PDF containing an excessively long Unicode sequence in the ActualText attribute, which when parsed by vulnerable Xpdf code triggers the out-of-bounds write; given the local vector and high complexity, exploitation typically requires the victim to open the file locally.

How to fix it

Upgrade Xpdf to the newest release that corrects ActualText buffer handling; if no newer package is available, replace Xpdf with an alternative PDF renderer until a fix is obtained.

How to confirm the fix worked

Reproduce with test PDFs containing long ActualText sequences and confirm absence of crashes or memory errors after applying updates; scan source or binary for the vulnerable array-write logic in text extraction routines.

Typical attack path

1. Craft malicious PDF embedding oversized ActualText Unicode sequence
2. Deliver the PDF via email, download, or shared storage
3. Victim opens the file using Xpdf or an application linking the library
4. Parser processes the sequence and performs the out-of-bounds write
5. Resulting memory corruption causes application crash or limited instability

How to detect it

Review system and application logs for Xpdf segmentation faults or abnormal exits immediately after PDF file access; inspect recent PDF files opened by users for suspicious text attributes.

What your security team should do

• Prioritize upgrade of Xpdf installations across the environment
• Block or sandbox untrusted PDF files from being processed by Xpdf
• Add Xpdf crash monitoring to endpoint detection rules
• Evaluate removal of Xpdf where alternative viewers are feasible