CVE-2020-14040 in Google
Summary
by MITRE
Go version v0.3.3 of the x/text package fixes a vulnerability in encoding/unicode that could lead to the UTF-16 decoder entering an infinite loop, causing the program to crash or run out of memory. An attacker could provide a single byte to a UTF16 decoder instantiated with UseBOM or ExpectBOM to trigger an infinite loop if the String function on the Decoder is called, or the Decoder is passed to golang.org/x/text/transform.String.
Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.
Analysis
by VulDB Data Team • 05/20/2025
The vulnerability identified as CVE-2020-14040 affects the go language x/text package version v0.3.3 and specifically targets the encoding/unicode component where a flaw exists in the UTF-16 decoder implementation. This issue manifests when the decoder encounters specific byte sequences that cause it to enter an infinite loop state, leading to program termination or severe memory exhaustion. The vulnerability is particularly concerning because it can be triggered through seemingly benign input data, making it difficult to detect during normal application testing phases. The affected decoder behavior occurs when instantiated with UseBOM or ExpectBOM parameters, which are commonly used in applications that need to handle various Unicode encoding formats. The flaw represents a classic denial of service vulnerability that can be exploited by malicious actors to disrupt service availability.
The technical root cause of this vulnerability lies in improper boundary checking within the UTF-16 decoder's state transition logic. When processing UTF-16 encoded data with specific byte patterns, the decoder fails to properly validate input sequences, causing it to repeatedly process the same input bytes without making forward progress. This condition is particularly dangerous when the String function is invoked on the decoder or when the decoder is passed to the transform.String function, as these operations typically involve extensive data processing. The infinite loop occurs because the decoder's internal state machine lacks proper termination conditions for malformed input sequences, allowing the processing to continue indefinitely until system resources are exhausted. This behavior aligns with CWE-835 which describes the weakness of infinite loops or infinite recursion in software implementations.
The operational impact of CVE-2020-14040 extends beyond simple program crashes, as it can lead to complete system resource exhaustion and denial of service conditions. Applications that process user-provided text data, especially those handling internationalized content or communicating with external systems that may provide malformed UTF-16 data, are at risk. The vulnerability affects systems running Go applications that utilize the x/text package for text processing, potentially impacting web applications, API services, and any software that relies on proper Unicode handling. Attackers can exploit this vulnerability by crafting malicious input that triggers the infinite loop condition, causing system instability and potentially enabling more sophisticated attacks through resource exhaustion. The vulnerability is particularly dangerous in environments where applications are not properly sandboxed or where multiple concurrent requests could amplify the impact of a single malicious input.
Mitigation strategies for CVE-2020-14040 primarily involve updating to the patched version of the Go x/text package, which addresses the underlying infinite loop condition in the UTF-16 decoder implementation. Organizations should prioritize updating their Go applications to versions that include the fix, typically Go 1.14.3 or later, which contain the necessary corrections to prevent the decoder from entering infinite loops. Additionally, implementing input validation and sanitization measures can provide defense-in-depth protection, ensuring that UTF-16 data is properly validated before being passed to the decoder. Security teams should also consider implementing resource limits and timeouts on text processing operations to prevent exploitation even if the primary fix is not immediately available. The vulnerability demonstrates the importance of proper state machine design in encoding libraries and highlights the need for comprehensive testing of edge cases in internationalization components, as outlined in ATT&CK technique T1499 which covers resource exhaustion tactics in cyber attacks.