CVE-2026-53505 in Thumbor
Summary
by MITRE • 07/31/2026
Thumbor is an open-source photo thumbnail service by globo.com. Prior to 7.8.0, Thumbor's filters:proportion(<value>) filter does not enforce an upper bound on <value> and runs in the post-transform phase. An attacker can trigger extremely large resizes (CPU/memory exhaustion) and cause denial of service. This issue is fixed in 7.8.0.
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Analysis
by VulDB Data Team • 07/31/2026
The Thumbor photo thumbnail service, developed by globo.com, experienced a critical vulnerability in its proportion filter functionality prior to version 7.8.0. This vulnerability stems from inadequate input validation within the filters:proportion filter which operates during the post-transform phase of image processing. The flaw allows attackers to specify arbitrary numeric values for the <value> parameter without proper upper bound enforcement, creating a pathway for malicious actors to manipulate the system's resource allocation mechanisms.
The technical implementation of this vulnerability resides in the insufficient sanitization of user-supplied parameters within the proportion filter's code execution flow. When an attacker submits a disproportionately large value to the proportion filter, the system processes this input without constraining the resulting image dimensions. This leads to exponential resource consumption as the service attempts to resize images to extremely large proportions, effectively creating a resource exhaustion attack vector that can be leveraged for denial of service operations.
The operational impact of this vulnerability extends beyond simple service disruption, as it represents a classic example of a resource exhaustion attack pattern that aligns with attack techniques documented in the MITRE ATT&CK framework under the resource exhaustion category. The vulnerability enables attackers to consume excessive CPU cycles and memory resources, potentially leading to complete system unavailability and affecting legitimate users who depend on the thumbnail service for image processing tasks. This type of vulnerability is particularly dangerous in cloud environments where resource consumption directly impacts operational costs and service availability.
The fix implemented in version 7.8.0 addresses this issue through proper input validation that enforces reasonable upper bounds on the proportion parameter values. This remediation aligns with security best practices for preventing denial of service attacks and follows established security controls such as those recommended in the CWE (Common Weakness Enumeration) catalog under weakness category CWE-400, which deals with resource exhaustion vulnerabilities. Organizations utilizing Thumbor should immediately upgrade to version 7.8.0 or later to mitigate this risk. The solution demonstrates proper defensive programming practices that include input validation and resource limiting mechanisms to prevent attackers from exploiting parameter manipulation for malicious resource consumption purposes.