CVE-2020-7060 in Communications Diameter Signaling Router
Summary
by MITRE
When using certain mbstring functions to convert multibyte encodings, in PHP versions 7.2.x below 7.2.27, 7.3.x below 7.3.14 and 7.4.x below 7.4.2 it is possible to supply data that will cause function mbfl_filt_conv_big5_wchar to read past the allocated buffer. This may lead to information disclosure or crash.
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Analysis
by VulDB Data Team • 10/31/2020
The vulnerability identified as CVE-2020-7060 represents a critical buffer overflow flaw within PHP's mbstring extension that affects multiple version ranges including php 7.2.x below 7.2.27, 7.3.x below 7.3.14, and 7.4.x below 7.4.2. This issue resides in the mbfl_filt_conv_big5_wchar function which handles multibyte character encoding conversions particularly for big5 encoding standards. The flaw manifests when specific mbstring functions process user-supplied data that contains malformed or specially crafted multibyte sequences. The underlying technical mechanism involves improper bounds checking during buffer operations where the function attempts to read memory locations beyond the allocated buffer boundaries. This buffer overread condition occurs specifically during the conversion process from big5 encoding to wchar format, creating a scenario where adjacent memory contents may be accessed and potentially exposed. The vulnerability falls under the CWE-125 vulnerability category which specifically addresses out-of-bounds read conditions, making it a direct implementation of improper input validation and memory handling practices.
The operational impact of this vulnerability extends beyond simple application instability to encompass potential information disclosure risks that could expose sensitive data residing in adjacent memory locations. When an attacker supplies maliciously crafted input to mbstring functions such as mb_convert_encoding, mb_convert_case, or other related conversion functions, the buffer overread condition can result in reading uninitialized memory, stack contents, or heap data that may contain credentials, session tokens, or other confidential information. The vulnerability can also lead to application crashes or denial of service conditions that disrupt legitimate service availability. This makes the flaw particularly dangerous in web applications where user input is processed through mbstring functions, as attackers can exploit this to either extract sensitive information or cause service disruption. The vulnerability is classified under the ATT&CK technique T1059.007 for command and scripting interpreter with potential for information gathering through memory exposure.
Mitigation strategies for CVE-2020-7060 require immediate patching of affected PHP installations to versions that contain the necessary security fixes. Organizations should prioritize updating their PHP environments to the latest stable releases within the supported version lines, specifically ensuring php 7.2.27, 7.3.14, and 7.4.2 or higher. Additionally, input validation should be implemented at application boundaries to sanitize all user-provided data before processing through mbstring functions, particularly when dealing with multibyte character encodings. Network segmentation and application firewalls can provide additional layers of protection by monitoring for suspicious input patterns that may indicate exploitation attempts. Security monitoring should include detection of unusual memory access patterns or application crashes that may indicate exploitation attempts. The vulnerability highlights the importance of proper bounds checking in memory operations and demonstrates how seemingly benign encoding conversion functions can become attack vectors when proper input validation is absent. Organizations should also implement regular security assessments and penetration testing to identify similar vulnerabilities in their PHP applications and ensure that all third-party libraries and extensions are kept up to date with security patches.