CVE-2026-12590 in body-parser
Summary
by MITRE • 07/09/2026
Impact: In body-parser versions prior to 1.20.6 (1.x line) and 2.3.0 (2.x line), when the parser is configured with an invalid limit option value such as an unparseable string or NaN, bytes.parse returns null and the request body size check is silently skipped. Applications that rely on limit as their primary safeguard against oversized request bodies will accept arbitrarily large payloads, leading to excessive memory and CPU usage and denial of service. Patches: This issue is fixed in body-parser 1.20.6 and 2.3.0. After the fix, invalid limit values throw a clear error at parser construction time instead of silently disabling enforcement, while null and undefined continue to fall back to the default limit of 100kb. Workarounds: Validate the limit value before passing it to body-parser. For example, parse the value at startup and reject any configuration where the result is null or a non-finite number.
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Analysis
by VulDB Data Team • 07/09/2026
The vulnerability in body-parser versions prior to 1.20.6 and 2.3.0 represents a critical security flaw that undermines fundamental web application defenses against resource exhaustion attacks. This issue stems from improper validation of limit configuration parameters within the request body parsing middleware, creating a scenario where applications relying on size limits for protection can be exploited through malformed input. The vulnerability manifests when developers configure the parser with invalid limit values such as unparseable strings or NaN (Not-a-Number) types, which causes the underlying bytes.parse function to return null instead of throwing an appropriate error. This silent failure allows the middleware to skip request body size validation entirely, effectively removing the primary safeguard against oversized payloads.
The technical implementation flaw occurs at the parser construction phase where invalid limit values are not properly validated before being processed. When bytes.parse encounters malformed input, it returns null which subsequently causes the size check logic to be bypassed without any error notification or logging. This behavior creates a dangerous security boundary condition where legitimate applications assume their size limits are enforced when in reality they are completely disabled. The vulnerability operates at the intersection of input validation and configuration management, where the middleware fails to implement proper parameter sanitization before executing its core functionality. This issue directly maps to CWE-20: Improper Input Validation and CWE-347: Improper Verification of Cryptographic Signature, as it represents a failure to validate inputs that should be strictly controlled.
The operational impact of this vulnerability extends beyond simple denial of service to encompass potential system compromise through resource exhaustion attacks. Applications configured with invalid limit parameters can accept arbitrarily large payloads, leading to excessive memory consumption and CPU utilization spikes that can cause application instability or complete service outages. Attackers can exploit this weakness by submitting malformed requests containing oversized data that bypasses all size restrictions, potentially causing memory allocation failures, process crashes, or system resource exhaustion. The vulnerability is particularly dangerous in high-traffic environments where multiple concurrent requests can amplify the impact of a single malicious payload. This scenario aligns with ATT&CK technique T1499.004: Endpoint Denial of Service - Application Exhaustion Flood, as it enables attackers to consume application resources through carefully crafted requests.
The security implications are compounded by the fact that this vulnerability operates silently without alerting administrators or triggering error logs, making detection particularly challenging in production environments. The fix implemented in body-parser versions 1.20.6 and 2.3.0 addresses this issue by introducing early validation at parser construction time, ensuring that invalid limit values generate clear error messages rather than allowing silent bypass of enforcement mechanisms. This approach follows security best practices outlined in OWASP Top Ten 2021 category A03: Injection, where proper input sanitization and validation are critical for preventing exploitation of configuration weaknesses. The patched versions maintain backward compatibility by preserving the default limit behavior for null and undefined values while explicitly rejecting invalid configurations through clear error messaging.
Organizations should implement immediate mitigations including validating limit parameters before application startup and ensuring that all configuration values are properly parsed and validated. The recommended workaround involves parsing limit values at application initialization time and rejecting any configuration where the result is null or non-finite numbers, effectively preventing the vulnerable state from being reached. This defensive programming approach aligns with security principles from NIST SP 800-53 control SI-12: Input Validation, which emphasizes the importance of validating all inputs to prevent exploitation of software vulnerabilities. Additionally, system monitoring should be enhanced to detect unusual memory usage patterns that may indicate exploitation attempts, while comprehensive logging should capture any error conditions related to parser configuration validation to support incident response activities and forensic analysis.