CVE-2026-42500: BMP Palette Index Out-of-Range Denial-of-Service Vulnerability

Technical summary

This vulnerability exists in BMP file parsing logic that fails to validate palette indices before accessing the underlying color lookup table. When a paletted BMP file contains pixel data with out-of-range palette indices, the decoding routine panics—typically a memory access violation or uncaught exception—rather than implementing bounds checking or error recovery. The attack surface is any application or service that automatically decodes BMP images without prior validation.

Business impact

Organizations relying on document processing pipelines, imaging services, or automated file handling systems face service disruption risk. A denial-of-service condition could interrupt business workflows, impact cloud-hosted image processing services, or affect user-facing applications that handle image uploads. The vulnerability is not an information disclosure or integrity issue, limiting its severity, but availability impact can still be material depending on the affected system's criticality.

Affected systems

The vulnerability affects BMP decoding implementations. Specific vendor and product information is not currently available in the public advisory data; organizations must verify which of their software dependencies include vulnerable BMP parsing logic. Common exposure points include image processing libraries, document converters, media players, and web applications with image upload or preview features.

Exploitability

Exploitation requires only network access and the ability to deliver a malicious BMP file to the target application—no authentication, privilege escalation, or user interaction beyond the act of opening or processing the file is needed. The CVSS vector (AV:N/AC:L/PR:N/UI:N) confirms low attack complexity and no prerequisites. However, practical impact depends on whether the affected application is exposed to untrusted image sources and whether a crash translates to meaningful service disruption in the deployment context.

Remediation

Patch the affected BMP decoding library or application immediately upon availability from the vendor. As an interim mitigation, implement file validation at ingestion points—reject or quarantine BMP files with suspicious characteristics, or disable automatic BMP processing if feasible. Apply input filtering to limit exposure to untrusted image sources.

Patch guidance

Contact the vendor or monitor their security advisories for a patched version that includes proper palette index bounds checking. Verify patch applicability to your specific product version before deployment. Test the update in a non-production environment to ensure compatibility with existing workflows.

Detection guidance

Monitor application logs and system event logs for sudden, unexplained crashes or restarts coinciding with BMP file processing. Network-based detection is limited but packet inspection for malformed BMP headers may flag suspicious files. Endpoint detection should focus on unexpected termination of image processing or document handling services when BMP files are accessed.

Why prioritize this

Although CVSS 5.3 (MEDIUM) reflects availability impact only, prioritization should account for your organizational exposure: (1) whether your applications or services process BMP files from untrusted sources; (2) whether crashes in those services trigger critical workflows or SLAs; (3) the ease of weaponization—a single malicious BMP file can be widely distributed. If BMP processing is endemic in your environment or supports customer-facing services, elevate priority accordingly.

Risk score, explained

A CVSS score of 5.3 reflects a denial-of-service vulnerability with low attack complexity and no authentication required, but no confidentiality or integrity impact. The score appropriately penalizes the lack of a pre-authentication requirement and straightforward exploitation path. However, CVSS is context-agnostic; the actual risk to your organization depends on whether exposed systems process untrusted BMP files and the business cost of unavailability in those systems.

Frequently asked questions