CVE-2020-37280 in cbor-sync
Summary
by MITRE • 10/12/2026
cbor-sync through 1.0.4 contains a resource exhaustion vulnerability in CBOR.decode that trusts declared array and map lengths without checking remaining input. Remote attackers can supply a tiny crafted CBOR payload declaring huge lengths to drive billions of iterations, exhausting CPU and process memory.
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Analysis
by VulDB Data Team • 10/12/2026
The cbor-sync library, specifically through version 1.0.4, contains a critical resource exhaustion vulnerability within its CBOR decoding functionality that stems from an improper validation of input data length declarations. This flaw is categorized under CWE-787: Out-of-bounds Write and more broadly as CWE-400: Uncontrolled Resource Consumption. The core technical issue arises because the decoder trusts the length fields declared in the Concise Binary Object Representation (CBOR) format without verifying whether sufficient bytes remain in the input stream to satisfy those declarations. CBOR is a binary data serialization format that uses self-describing tags, allowing for efficient encoding of complex structures like arrays and maps by specifying their lengths upfront. In this vulnerable implementation, when an attacker provides a crafted payload with extremely large length values for an array or map structure, the decoder proceeds to allocate memory and iterate based on these unverified numbers rather than checking against the actual size of the provided input buffer.
This architectural oversight allows remote attackers to exploit the vulnerability by sending minimal but maliciously constructed CBOR payloads that declare massive sizes for data structures. Upon receiving such a payload, the library attempts to process the declared length, leading to billions of iterations or memory allocation requests depending on the internal implementation details. This behavior results in severe performance degradation as the system consumes excessive CPU cycles attempting to parse non-existent data elements. Furthermore, if the underlying logic involves dynamic memory allocation proportional to the declared size before validation checks are completed, it can lead to significant process memory exhaustion. The impact is particularly acute because CBOR is often used in constrained environments and high-throughput scenarios where efficiency is paramount, making this library a potential target for denial-of-service attacks aimed at destabilizing services that rely on cbor-sync for data serialization tasks.
The operational impact of this vulnerability includes complete service unavailability due to resource starvation. Systems processing untrusted CBOR input are susceptible to being overwhelmed by these crafted packets, leading to crashes or indefinite hangs as the application waits for resources that will never materialize from the truncated input. This aligns with MITRE ATT&CK technique T1496: Resource Hijacking, where attackers consume computational resources to degrade service availability. The lack of bounds checking during the decoding phase means that even a small network packet can trigger disproportionate resource consumption on the server side, effectively turning a lightweight serialization library into an attack vector for distributed denial-of-service (DDoS) attacks if exposed via APIs or message queues.
To mitigate this vulnerability, immediate updates to cbor-sync version 1.0.5 or later are required, as these versions implement proper bounds checking before processing declared lengths. Developers integrating older versions should enforce strict input validation at the application layer by verifying that the total payload size matches the sum of its structural components before passing it to the decoder. Additionally, implementing rate limiting and connection timeouts can help mitigate the impact of such attacks in production environments. It is also recommended to audit other serialization libraries for similar patterns where declared lengths are not validated against actual input sizes, ensuring robust defense-in-depth strategies against resource exhaustion exploits.