CVE-2020-29511 in Google
Summary
by MITRE • 12/15/2020
The encoding/xml package in Go (all versions) does not correctly preserve the semantics of element namespace prefixes during tokenization round-trips, which allows an attacker to craft inputs that behave in conflicting ways during different stages of processing in affected downstream applications.
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Analysis
by VulDB Data Team • 12/17/2020
The vulnerability identified as CVE-2020-29511 resides within the encoding/xml package of the Go programming language, affecting all versions of the language. This issue stems from improper handling of namespace prefix semantics during XML tokenization processes, creating a fundamental flaw in how XML documents are parsed and reconstructed. The core problem manifests when XML elements contain namespace declarations that are not consistently maintained throughout the round-trip processing cycle, where data flows from parsing to serialization and back again. This inconsistency creates a potential attack surface where maliciously crafted XML inputs can exploit the flawed namespace handling to produce unexpected behavioral outcomes in applications that rely on proper XML processing semantics.
The technical implementation of this vulnerability exploits the way Go's XML parser manages namespace prefixes during tokenization operations. When an XML document is parsed and subsequently serialized, the namespace prefix mappings may not be preserved accurately, leading to scenarios where elements that should maintain their original namespace context are altered during the processing cycle. This behavior creates a discrepancy between the parsed representation and the serialized output, particularly affecting elements that depend on specific namespace prefix bindings. The flaw occurs at the tokenization level where namespace information is not consistently maintained across parsing and serialization operations, allowing attackers to manipulate XML structures in ways that can cause downstream applications to interpret data incorrectly.
The operational impact of CVE-2020-29511 extends beyond simple parsing failures to potentially enable more sophisticated attacks depending on how affected applications process XML data. Applications that rely on namespace prefix semantics for proper XML document interpretation may experience unexpected behavior when processing inputs that exploit this vulnerability. The vulnerability can lead to security issues in systems that perform XML-based configuration management, data exchange, or document processing where namespace handling is critical for proper operation. Attackers can craft XML inputs that appear valid during parsing but produce different semantic interpretations when serialized, potentially allowing for bypassing security checks, manipulating application logic, or causing denial of service conditions in systems that depend on consistent XML processing behavior.
This vulnerability aligns with CWE-1004 which addresses insecure default settings and CWE-116 which covers improper encoding or escaping of data. The issue also maps to ATT&CK technique T1059.007 for XML external entity processing and T1566 for malicious file execution through XML processing. Organizations using Go applications that process XML data should prioritize updating to patched versions of the Go language, as the vulnerability affects the core XML processing capabilities that are fundamental to many applications. Mitigation strategies include implementing additional input validation checks, monitoring XML processing operations for anomalous behavior, and ensuring that applications properly handle namespace prefix semantics during XML operations. The vulnerability demonstrates the importance of maintaining semantic consistency in data processing pipelines and highlights the need for thorough testing of XML handling capabilities in security-critical applications.