CVE-2011-0101 in Excel
Summary
by MITRE
Microsoft Excel 2002 SP3 allows remote attackers to execute arbitrary code or cause a denial of service (memory corruption) via a crafted RealTimeData record, related to a stTopic field, doubly-byte characters, and an incorrect pointer calculation, aka "Excel Record Parsing WriteAV Vulnerability."
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Analysis
by VulDB Data Team • 11/02/2021
The vulnerability identified as CVE-2011-0101 represents a critical memory corruption flaw within Microsoft Excel 2002 Service Pack 3 that enables remote attackers to achieve arbitrary code execution or cause denial of service conditions. This vulnerability specifically targets the Excel record parsing mechanism, particularly focusing on the RealTimeData record structure that handles real-time data updates within spreadsheet applications. The flaw manifests through improper handling of the stTopic field within this record type, combined with processing of doubly-byte character sequences that are commonly used in internationalized text processing. The vulnerability's root cause lies in an incorrect pointer calculation that occurs during the parsing of these specific record structures, creating a condition where attacker-controlled data can overwrite critical memory locations.
The technical exploitation of this vulnerability follows a well-defined pattern that aligns with CWE-121, which describes heap-based buffer overflow conditions, and CWE-787, which addresses out-of-bounds write vulnerabilities. Attackers craft malicious Excel files containing specially formatted RealTimeData records with malformed stTopic fields and doubly-byte character sequences that trigger the flawed pointer arithmetic. When Excel processes these records, the incorrect pointer calculation causes memory corruption that can be leveraged for arbitrary code execution through stack or heap overflows. The vulnerability's classification as a writeAV (write arbitrary value) vulnerability indicates that the attacker can control the memory locations being overwritten, potentially leading to privilege escalation or complete system compromise.
From an operational impact perspective, this vulnerability presents significant risks to enterprise environments where Excel 2002 remains in use, particularly in legacy systems that have not been migrated to newer versions. The attack vector is highly effective as it requires no user interaction beyond opening the malicious file, making it suitable for phishing campaigns or automated exploitation. The vulnerability's potential for denial of service means that even successful exploitation without code execution can render systems unusable, causing business disruption. Organizations running older Excel versions face particular risk as these systems often lack modern exploit mitigation features such as address space layout randomization and data execution prevention that are standard in newer Office releases.
The exploitation of this vulnerability aligns with ATT&CK technique T1203, which describes exploitation of remote services, and T1059, which covers command and control through scripting. The attack chain typically involves delivery of the malicious Excel file through email attachments, web downloads, or infected removable media. Upon opening the file, Excel's parsing engine processes the malformed RealTimeData record, triggering the memory corruption that can be leveraged for privilege escalation. Microsoft's security advisory for this vulnerability recommends immediate patching through the Microsoft Security Response Center, as well as implementing network-based protections such as email filtering and application whitelisting to prevent execution of untrusted Office files. Organizations should also consider implementing user education programs to reduce the risk of accidental file execution, as this vulnerability can be effectively exploited through social engineering techniques that target end users through convincing phishing campaigns.