The vulnerability CVE-2025-68131 affects the agronholm cbor2 Python library, which implements encoding and decoding for the Concise Binary Object Representation (CBOR) format. CBOR is a binary data serialization format commonly used in IoT, embedded systems, and network protocols due to its compactness and efficiency. Starting from version 3.0.0 and prior to 5.8.0, the CBORDecoder class in cbor2 exhibits improper handling of shared references when decoder instances are reused. Specifically, values tagged with the shareable tag (28) persist in the decoder's internal memory state after decoding a message. Subsequent CBOR messages that include sharedref tags (29) can access these lingering values. This behavior violates the principle of proper removal of sensitive information before storage or transfer, classified under CWE-212. An attacker who can supply malicious CBOR messages to a system that reuses a CBORDecoder instance across trust boundaries can exploit this flaw to read sensitive data from previously decoded messages. The vulnerability requires no authentication or user interaction and can be exploited remotely if the attacker can send crafted CBOR data to the vulnerable decoder. The flaw is patched in cbor2 version 5.8.0, which ensures that shared values do not persist across decode operations. No known exploits are currently reported in the wild. The CVSS 4.0 base score is 5.5 (medium severity), reflecting the moderate impact on confidentiality with no impact on integrity or availability, and ease of exploitation without privileges or user interaction.

For European organizations, the primary impact of CVE-2025-68131 is the potential leakage of sensitive information processed via CBOR serialization. This is particularly relevant for sectors relying on Python-based services or IoT devices that use cbor2 for data interchange. Confidential data from previous decoding operations can be exposed to attackers who can send malicious CBOR messages, leading to breaches of privacy, intellectual property theft, or exposure of credentials and tokens. This risk is heightened in multi-tenant environments, cloud services, or any system where CBORDecoder instances are reused across different trust domains. While the vulnerability does not affect data integrity or system availability, the confidentiality breach could lead to regulatory non-compliance under GDPR and damage organizational reputation. The medium severity score reflects the moderate but non-trivial risk, especially in environments processing sensitive or regulated data.

The most effective mitigation is to upgrade the agronholm cbor2 library to version 5.8.0 or later, where the vulnerability is patched. If immediate upgrade is not feasible, organizations should ensure that CBORDecoder instances are not reused across different trust boundaries; instead, instantiate a new decoder for each decoding operation to prevent shared state persistence. Additionally, input validation and strict access controls should be enforced to limit exposure to untrusted CBOR data sources. Security teams should audit codebases and IoT device firmware for usage of vulnerable cbor2 versions and implement monitoring for anomalous CBOR message patterns that could indicate exploitation attempts. Incorporating secure coding practices around serialization and deserialization, including memory clearing and object lifecycle management, will reduce risk. Finally, organizations should review their incident response plans to include scenarios involving serialization-based data leakage.