CVE-2024-46478: Htmldoc Buffer Overflow Vulnerability

CVE-2024-46478 Overview

A buffer overflow vulnerability has been identified in HTMLDOC v1.9.18, specifically within the parse_pre function located in ps-pdf.cxx at line 5681. HTMLDOC is a widely-used open-source application that converts HTML and Markdown source files into various output formats including PostScript and PDF. This vulnerability allows remote attackers to potentially achieve code execution or cause denial of service through specially crafted input files.

Critical Impact
This buffer overflow vulnerability in HTMLDOC v1.9.18 can be exploited remotely without authentication, potentially allowing attackers to execute arbitrary code or crash the application when processing malicious HTML documents.

Affected Products

HTMLDOC v1.9.18
htmldoc_project htmldoc

Discovery Timeline

2024-10-24 - CVE-2024-46478 published to NVD
2025-06-24 - Last updated in NVD database

Technical Details for CVE-2024-46478

Vulnerability Analysis

This vulnerability is classified as CWE-120 (Buffer Copy without Checking Size of Input), commonly known as a classic buffer overflow. The flaw exists in the parse_pre function within the ps-pdf.cxx source file, which handles preformatted text blocks during HTML to PDF/PostScript conversion.

The core issue stems from improper boundary checking when processing tab characters within preformatted text. When the function encounters tab characters, it expands them into spaces, but the original boundary check did not account for the maximum possible expansion size of a tab character (up to 8 spaces). This oversight allows data to be written beyond the allocated buffer boundaries.

The vulnerability is exploitable over the network as HTMLDOC can process remotely-sourced HTML files, and exploitation requires no authentication or user interaction beyond triggering the document conversion process.

Root Cause

The root cause is insufficient buffer boundary validation in the parse_pre function when handling tab character expansion. The original code used a boundary check of sizeof(line) - 1, which failed to account for the fact that a single tab character can expand to multiple space characters (up to 8). This miscalculation creates a condition where the buffer can overflow when processing input containing tab characters near the end of the allocated buffer space.

Attack Vector

An attacker can exploit this vulnerability by crafting a malicious HTML document containing preformatted text (<pre> blocks) with strategically placed tab characters. When HTMLDOC processes this document to convert it to PDF or PostScript format, the buffer overflow occurs during tab expansion, potentially allowing:

Remote Code Execution: Overwriting return addresses or function pointers to redirect execution flow
Denial of Service: Crashing the application through memory corruption
Information Disclosure: Leaking sensitive memory contents in certain scenarios

The attack can be delivered through any workflow that processes untrusted HTML documents with HTMLDOC, including web applications, document conversion services, or automated document processing pipelines.

text

 
 	case MARKUP_NONE :
             for (lineptr = line, dataptr = start->data;
-		 *dataptr != '\0' && lineptr < (line + sizeof(line) - 1);
+		 *dataptr != '\0' && lineptr < (line + sizeof(line) - 9);
 	         dataptr ++)
+	    {
               if (*dataptr == '\n')
+              {
 		break;
+              }
               else if (*dataptr == '\t')
               {
                /* This code changed after 15 years to work around new compiler optimization bugs (Issue #349) */

Source: GitHub Commit 683bec5

The patch changes the boundary check from sizeof(line) - 1 to sizeof(line) - 9, reserving sufficient space for the maximum tab expansion (8 characters) plus the null terminator.

Detection Methods for CVE-2024-46478

Indicators of Compromise

Unexpected crashes or segmentation faults in HTMLDOC processes during document conversion
Abnormal memory usage patterns when processing HTML files with preformatted text blocks
Core dumps or crash logs referencing parse_pre function or ps-pdf.cxx
Unusual HTML files containing excessive or strategically placed tab characters in <pre> blocks

Detection Strategies

Monitor HTMLDOC process behavior for abnormal terminations or memory access violations
Implement file integrity monitoring on HTMLDOC binaries to detect unauthorized modifications
Deploy application-level logging to capture conversion failures and error conditions
Use static analysis tools to identify vulnerable HTMLDOC versions in your environment

Monitoring Recommendations

Audit systems for installations of HTMLDOC version 1.9.18 using software inventory tools
Enable core dump analysis for early detection of exploitation attempts
Monitor for unusual patterns in HTML document submissions to conversion services
Implement input validation for HTML files before processing with HTMLDOC

How to Mitigate CVE-2024-46478

Immediate Actions Required

Update HTMLDOC to a patched version that includes commit 683bec548e642cf4a17e003fb34f6bbaf2d27b98
Audit systems for vulnerable HTMLDOC v1.9.18 installations
Restrict access to HTMLDOC conversion services to trusted users only
Implement input sanitization for HTML files before processing

Patch Information

The vulnerability has been addressed by the HTMLDOC project maintainer through a security commit. The fix modifies the boundary check in the parse_pre function to properly account for tab character expansion, changing the buffer limit from sizeof(line) - 1 to sizeof(line) - 9. Organizations should apply the patch available in the GitHub commit or upgrade to a version that includes this fix.

Workarounds

Restrict HTMLDOC usage to trusted, internally-generated HTML documents only
Implement a preprocessing step to strip or replace tab characters from HTML input files
Run HTMLDOC in a sandboxed environment with limited system access
Disable or limit access to document conversion services using vulnerable HTMLDOC versions

bash

# Check installed HTMLDOC version
htmldoc --version

# Example: Strip tabs from HTML before processing (temporary workaround)
sed 's/\t/        /g' input.html > sanitized.html
htmldoc sanitized.html -f output.pdf