veraPDF Parser DoS via PostScript CMap Streams

Summary

Description

A PostScript-interpreter-driven Denial of Service (CWE-1325) vulnerability in veraPDF allows a remote attacker to exhaust validator memory or CPU by submitting a PDF whose Type 0 font /Encoding (or any /ToUnicode) is a CMap stream containing attacker-supplied PostScript. veraPDF reuses its CMap parser as a general PostScript interpreter and exposes the unguarded array N allocation operator and the for control operator with no zero-increment guard. This affects all current versions of veraPDF-parser.

Details

The vulnerability resides in veraPDF-parser. CMap streams referenced as a Type 0 font's /Encoding (or any font's /ToUnicode) are parsed by CMapParser (veraPDF-parser/src/main/java/org/verapdf/pd/font/cmap/CMapParser.java), which extends PSParser. Tokens that are not the small CMap-specific keyword set (begincodespacerange, bfchar, cidchar, ...) fall through to PSObject.execute (veraPDF-parser/src/main/java/org/verapdf/parser/postscript/PSObject.java), which dispatches generic PostScript operators implemented in PSOperator (veraPDF-parser/src/main/java/org/verapdf/parser/postscript/PSOperator.java).

Two operators in that interpreter take their bound from the PDF and apply no validation:

1. array at PSOperator.java:536-547 pops the top number from the operand stack and immediately calls COSArray.construct(arraySize), then loops arraySize times appending COSObject.getEmpty(). COSArray.construct(int) calls new ArrayList<>(arraySize) (COSArray.java:102), so the underlying Object[] is allocated up-front. Passing 2147483647 (Integer.MAX_VALUE) requests a 16 GB backing array on a 64-bit JVM.
2. for at PSOperator.java:571-592 reads initial, increment, and limit from the stack and loops for (long i = initial; i <= limit; i += increment). Because increment is unchecked, 0 0 1 { } for produces an infinite-CPU spin (and progressively a heap exhaustion as each iteration pushes i onto the operand stack).

CMapFactory.getCMap only catches IOException and PostScriptException; it does not catch OutOfMemoryError or wall-clock budget, so the failure propagates out of font model construction and aborts the validation worker.

A single payload byte sequence, the unframed PostScript 2147483647 array, is sufficient. No begincmap/endcmap framing is required because the operator runs before the parser ever reaches the CMap structure.

Impact

This impacts all current releases of the veraPDF-parser. Successful exploitation requires only that the target validate an attacker-supplied PDF; a single Type 0 font with a malicious /Encoding (or any /ToUnicode) stream is sufficient.

Proposed Patch

Cap array allocation and forbid zero increments in for.

As a defensive measure, also wrap CMapFactory.getCMap to enforce a wall-clock and operand-stack-size budget on CMap parsing, and audit the remaining unbounded operators (copy, roll, dict) for similar primitives.