CVE-2026-107621 in dcm4chee-arc-light
Summary
by MITRE • 10/16/2026
JPEGParser can enter an infinite loop while parsing a specially crafted or truncated stream.
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Analysis
by VulDB Data Team • 10/16/2026
The vulnerability identified in the JPEGParser component represents a critical flaw in the input validation and state machine logic used for processing Joint Photographic Experts Group image files. This issue manifests as an infinite loop, which occurs when the parser encounters specific malformed data structures within a specially crafted or truncated stream. In standard operation, parsers are designed to iterate through file headers, markers, and compressed data segments until they reach the end of the valid content or encounter a termination marker. However, in this instance, the logic fails to properly detect invalid sequences or unexpected truncations that cause the parsing state machine to revert to a previous state without advancing the read pointer or breaking out of the loop. This creates a scenario where the application consumes 100 percent of available CPU resources on the affected thread indefinitely, effectively rendering it unresponsive to further input or system events.
From a technical perspective, this flaw is characteristic of improper validation of boundary conditions and lack of robust error handling during stream parsing. When a JPEG file is truncated, critical markers that signal the end of data segments may be missing. A well-secured parser should detect these anomalies early and abort processing with an appropriate error code rather than attempting to interpret incomplete or corrupted data structures as valid sequences. The absence of such safeguards allows malicious actors to craft files where specific marker combinations or byte patterns trigger recursive logic errors or tight loops that never satisfy the exit condition. This is particularly dangerous in environments where image parsing occurs on a main thread, as it can freeze entire user interfaces, and equally hazardous in server-side applications handling multiple concurrent requests, leading to rapid resource exhaustion across the system.
The operational impact of this vulnerability extends beyond simple application instability. In client-side software, such as photo viewers or web browsers with embedded rendering engines, an infinite loop caused by a malicious JPEG file can lead to denial of service for the end user, requiring manual intervention via task managers to terminate the process. For server-side applications that automatically ingest and process uploaded images, this vulnerability poses a severe risk of resource exhaustion attacks. An attacker could send multiple requests containing these crafted streams simultaneously, causing CPU saturation across all worker threads handling image processing. This effectively denies service to legitimate users attempting to upload or view content, constituting a significant availability compromise. Furthermore, in some complex implementations, such infinite loops can serve as precursors to more severe exploits by allowing attackers to manipulate memory states over extended periods, potentially leading to heap corruption or other memory-related vulnerabilities if the loop interacts with dynamic allocation routines.
This vulnerability aligns closely with Common Weakness Enumeration (CWE) categories related to input validation and resource management. Specifically, it falls under CWE-835: Loop with Unreachable Exit Condition, also known as an infinite loop, which describes situations where a program enters a repetitive sequence that never terminates due to flawed logic or missing exit criteria. Additionally, the failure to properly handle malformed input relates to CWE-20: Improper Input Validation, indicating that the parser does not adequately sanitize or verify the structural integrity of the JPEG stream before processing its contents. From an offensive security perspective, this behavior can be mapped to MITRE ATT&CK techniques involving resource exhaustion and denial of service, where adversaries leverage software bugs to disrupt operational continuity without necessarily gaining unauthorized access to data or system controls.
Mitigation strategies must focus on hardening the parsing logic against malformed inputs. Developers should implement strict length checks for all variable-length fields within the JPEG structure and ensure that every loop has a definitive exit condition based on both valid termination markers and maximum iteration limits as a safety net. It is crucial to validate that stream pointers do not regress or stall during processing, ensuring forward progress with each byte read. Additionally, integrating timeout mechanisms at the application level can provide an additional layer of defense by forcibly terminating any parsing operation that exceeds expected duration thresholds. Regular security audits focusing on state machine logic and fuzz testing against edge cases involving truncated files are essential to identify similar flaws before deployment. Updating to patched versions of the library or component containing JPEGParser is the immediate remediation step for existing deployments, while long-term resilience requires adopting robust input validation frameworks that adhere to secure coding standards for binary file parsing.