CVE-2026-22189: Panda3D Buffer Overflow Vulnerability

CVE-2026-22189 Overview

CVE-2026-22189 is a stack-based buffer overflow vulnerability in Panda3D's egg-mkfont utility affecting versions up to and including 1.10.16. The vulnerability arises from the use of an unbounded sprintf() call with attacker-controlled input when constructing glyph filenames. When a user supplies an excessively long glyph pattern via the -gp command-line parameter, the input is formatted into a fixed-size stack buffer without proper length validation, leading to memory corruption.

Critical Impact

Exploitation of this vulnerability results in a deterministic crash due to memory corruption. Depending on the build configuration and execution environment, the buffer overflow may also be exploitable for arbitrary code execution.

Affected Products

• Panda3D versions up to and including 1.10.16
• The egg-mkfont utility component

Discovery Timeline

• January 7, 2026 - CVE-2026-22189 published to NVD
• January 8, 2026 - Last updated in NVD database

Technical Details for CVE-2026-22189

Vulnerability Analysis

This vulnerability is classified as CWE-121 (Stack-based Buffer Overflow). The egg-mkfont tool, used for generating font assets in the Panda3D game engine, improperly handles user-supplied glyph pattern strings. The core issue lies in the filename construction logic where user input from the -gp (glyph pattern) command-line argument is passed directly to an unbounded sprintf() function call.

The function writes the formatted string to a fixed-size buffer allocated on the stack. Since no length checking is performed before or during the sprintf() operation, providing a glyph pattern string longer than the buffer size will cause the write operation to exceed the buffer boundaries. This overwrites adjacent stack memory, corrupting return addresses, saved registers, and other critical stack data.

Root Cause

The root cause is the use of sprintf() without boundary validation when processing the -gp command-line argument. The vulnerable code path constructs glyph filenames by formatting user input into a stack-allocated buffer of fixed size. The sprintf() function does not enforce any output length limits, making it inherently unsafe for handling untrusted input. Secure alternatives such as snprintf() with explicit buffer size limits should be used to prevent this class of vulnerability.

Attack Vector

The attack requires local access to invoke the egg-mkfont utility with a maliciously crafted -gp argument. An attacker must be able to execute the vulnerable binary and supply command-line arguments. The exploitation flow involves:

1. The attacker invokes egg-mkfont with an oversized glyph pattern string
2. The vulnerable sprintf() call writes beyond the stack buffer boundaries
3. Stack memory corruption occurs, overwriting critical data structures
4. The application crashes deterministically
5. In certain configurations, the overflow may allow control of the instruction pointer for arbitrary code execution

The vulnerability does not require any special privileges to trigger, and no user interaction beyond executing the command is necessary. However, the local attack vector limits the exposure compared to remotely exploitable vulnerabilities.

Detection Methods for CVE-2026-22189

Indicators of Compromise

• Unexpected crashes or segmentation faults when running egg-mkfont
• Core dumps showing stack corruption in glyph filename generation functions
• Abnormal command-line arguments to egg-mkfont with excessively long -gp values
• Process termination events for Panda3D-related utilities

Detection Strategies

• Monitor process execution for egg-mkfont invocations with unusually long command-line arguments
• Implement endpoint detection rules to flag command strings exceeding normal parameter lengths
• Deploy application crash monitoring to detect exploitation attempts resulting in segmentation faults
• Use static analysis tools to identify unsafe sprintf() usage in deployed binaries

Monitoring Recommendations

• Enable core dump collection for Panda3D utilities to facilitate post-incident analysis
• Configure logging for command-line arguments passed to development tools in build pipelines
• Implement file integrity monitoring on Panda3D installation directories
• Review build and asset generation logs for anomalous egg-mkfont executions

How to Mitigate CVE-2026-22189

Immediate Actions Required

• Upgrade Panda3D to a patched version when available from the vendor
• Restrict access to the egg-mkfont utility to trusted users only
• Avoid using untrusted input for the -gp parameter in automated workflows
• Consider removing or disabling egg-mkfont if font generation functionality is not required

Patch Information

As of the last NVD update on January 8, 2026, users should monitor the GitHub Panda3D Repository and Panda3D Official Website for security patches addressing this vulnerability. The VulnCheck Panda3D Advisory and Full Disclosure Mailing List Post provide additional technical details and remediation guidance.

Workarounds

• Implement input validation wrapper scripts that check -gp argument length before invoking egg-mkfont
• Use containerization or sandboxing to isolate egg-mkfont execution and limit potential impact
• Deploy application-level input filtering to reject glyph patterns exceeding reasonable length thresholds
• Compile Panda3D with stack canary protections and ASLR enabled to make exploitation more difficult

# Example wrapper script to validate -gp argument length
#!/bin/bash
MAX_PATTERN_LENGTH=256
for arg in "$@"; do
    if [[ ${#arg} -gt $MAX_PATTERN_LENGTH ]]; then
        echo "Error: Argument exceeds maximum allowed length"
        exit 1
    fi
done
/usr/bin/egg-mkfont "$@"