CVE-2005-1935 in Windows
Summary
by MITRE
Heap-based buffer overflow in the BERDecBitString function in Microsoft ASN.1 library (MSASN1.DLL) allows remote attackers to execute arbitrary code via nested constructed bit strings, which leads to a realloc of a non-null pointer and causes the function to overwrite previously freed memory, as demonstrated using a SPNEGO token with a constructed bit string during HTTP authentication, and a different vulnerability than CVE-2003-0818. NOTE: the researcher has claimed that MS:MS04-007 fixes this issue.
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Analysis
by VulDB Data Team • 09/17/2018
The vulnerability identified as CVE-2005-1935 represents a critical heap-based buffer overflow within Microsoft's ASN.1 library implementation, specifically affecting the BERDecBitString function in MSASN1.DLL. This flaw resides in the fundamental parsing mechanism responsible for decoding Basic Encoding Rules (BER) formatted data structures, which are extensively used in various security protocols including Kerberos and SPNEGO token processing. The vulnerability manifests when the library encounters nested constructed bit strings during the decoding process, creating a dangerous condition where memory management becomes compromised due to improper pointer handling during reallocation operations. The technical implementation flaw stems from the function's failure to properly validate the bounds of memory allocations when processing complex nested structures, leading to a scenario where a realloc operation targets a non-null pointer that has already been freed, creating a classic use-after-free condition that can be exploited to achieve arbitrary code execution.
The operational impact of this vulnerability extends beyond simple denial of service scenarios, as it enables remote code execution through carefully crafted malicious ASN.1 encoded data structures. Attackers can exploit this weakness by constructing SPNEGO tokens containing nested constructed bit strings that trigger the vulnerable code path during HTTP authentication processes, effectively allowing them to execute arbitrary code on affected systems with the privileges of the vulnerable application. This vulnerability demonstrates the dangerous intersection of cryptographic protocol implementation flaws and memory corruption vulnerabilities, as the attack vector leverages legitimate security protocols to deliver malicious payloads. The flaw specifically targets the memory management patterns within the ASN.1 decoder, where the realloc function call operates on memory that has already been freed, creating memory corruption that can be manipulated to overwrite critical program data or function pointers, ultimately allowing attackers to redirect execution flow.
From a cybersecurity perspective, this vulnerability aligns with CWE-122, which describes heap-based buffer overflow conditions, and demonstrates characteristics consistent with ATT&CK technique T1059.007 for command and script injection through malformed data processing. The vulnerability is particularly concerning because it operates at a low level within the security infrastructure, affecting core cryptographic libraries that multiple applications and services depend upon for secure communication. The fact that this vulnerability was demonstrated using SPNEGO tokens during HTTP authentication highlights its potential for widespread exploitation in web-based environments where authentication mechanisms are frequently targeted. The specific nature of the exploit requires attackers to understand both the ASN.1 encoding format and the internal memory management patterns of the vulnerable library, making it a sophisticated attack vector that requires careful crafting of malicious payloads to achieve successful exploitation.
Microsoft's response to this vulnerability was addressed through MS04-007, which provided a security update specifically targeting the memory corruption issue within the ASN.1 library. The patch corrected the improper memory management within the BERDecBitString function by implementing proper bounds checking and ensuring that realloc operations do not target previously freed memory regions. Organizations should prioritize applying this security update as it directly addresses the root cause of the vulnerability without requiring application-level workarounds or configuration changes. The vulnerability serves as a reminder of the critical importance of proper memory management in cryptographic libraries and the potential for seemingly benign parsing operations to create severe security risks when memory corruption is not properly handled. Security practitioners should monitor for similar patterns in other ASN.1 implementations and ensure that all applications relying on such libraries receive appropriate security updates to prevent exploitation of similar memory corruption vulnerabilities.