CVE-2021-29508 in Wire
Summary
by MITRE • 05/12/2021
Due to how Wire handles type information in its serialization format, malicious payloads can be passed to a deserializer. e.g. using a surrogate on the sender end, an attacker can pass information about a different type for the receiving end. And by doing so allowing the serializer to create any type on the deserializing end. This is the same issue that exists for .NET BinaryFormatter https://docs.microsoft.com/en-us/visualstudio/code-quality/ca2300?view=vs-2019. This also applies to the fork of Wire.
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Analysis
by VulDB Data Team • 05/13/2021
The vulnerability CVE-2021-29508 represents a critical deserialization flaw in the Wire serialization library that enables remote code execution through crafted malicious payloads. This issue stems from Wire's improper handling of type information during the serialization process, creating a dangerous attack vector where an attacker can manipulate type metadata to force the deserializer into creating unintended object types. The vulnerability specifically exploits how Wire processes surrogate types on the sender side, allowing attackers to inject type information that the receiving end interprets as legitimate type descriptors rather than malicious payloads.
The technical implementation of this vulnerability aligns with common deserialization attack patterns documented in CWE-502, which classifies deserialization of untrusted data as a severe security weakness. When Wire encounters serialized data containing surrogate type information, it fails to properly validate or sanitize the type metadata before attempting deserialization. This allows an attacker to craft payloads that, when processed by the deserializer, create arbitrary object instances in memory. The flaw mirrors the well-known issues found in .NET BinaryFormatter, which has been deprecated due to similar vulnerabilities as referenced in Microsoft's security guidance CA2300. The vulnerability exists not only in the original Wire library but also in its forks, indicating a widespread implementation issue across related serialization frameworks.
The operational impact of CVE-2021-29508 is severe and potentially catastrophic for systems relying on Wire for data serialization. Attackers can leverage this vulnerability to execute arbitrary code on vulnerable systems, potentially leading to complete system compromise, data exfiltration, or privilege escalation. The attack requires minimal privileges to initiate, as it operates at the application level during data processing rather than requiring system-level access. Systems using Wire for inter-process communication, network data exchange, or persistent storage are all at risk, particularly when processing untrusted data from external sources. The vulnerability is particularly dangerous in environments where Wire is used for RPC communications, microservices integration, or any scenario involving data exchange between untrusted parties.
Mitigation strategies for CVE-2021-29508 must address both immediate remediation and long-term architectural improvements. Organizations should prioritize updating to patched versions of Wire or its forks as soon as available, while implementing strict input validation and sanitization measures for all deserialization operations. The recommended approach aligns with ATT&CK technique T1203, which emphasizes preventing malicious code execution through proper input validation. Additional protective measures include implementing type whitelisting for deserialization processes, using alternative serialization formats that do not suffer from similar type confusion issues, and employing application-level firewalls or proxies to filter incoming serialized data. Security teams should also consider implementing runtime monitoring and anomaly detection to identify potential exploitation attempts, as the vulnerability may be used in conjunction with other attack vectors to establish persistent access to affected systems.