CVE-2016-10091 in unrtf
Summary
by MITRE
Multiple stack-based buffer overflows in unrtf 0.21.9 allow remote attackers to cause a denial-of-service by writing a negative integer to the (1) cmd_expand function, (2) cmd_emboss function, or (3) cmd_engrave function.
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Analysis
by VulDB Data Team • 09/19/2020
The vulnerability identified as CVE-2016-10091 represents a critical stack-based buffer overflow issue affecting the unrtf 0.21.9 software library. This flaw exists within the handling of RTF document processing functions, specifically targeting three distinct command processing functions that are responsible for text formatting operations. The vulnerability stems from improper input validation mechanisms that fail to properly sanitize integer values before using them as array indices or buffer sizes. When maliciously crafted RTF documents are processed by the vulnerable software, attackers can manipulate the cmd_expand, cmd_emboss, and cmd_engrave functions to write negative integer values that subsequently trigger buffer overflow conditions in the stack memory allocation.
The technical exploitation of this vulnerability occurs through the manipulation of integer parameters within the RTF parsing pipeline where these functions receive unvalidated input data. The negative integer values cause the software to attempt memory allocations or array indexing operations that exceed the bounds of allocated stack buffers, leading to memory corruption and potential arbitrary code execution. This type of vulnerability falls under the Common Weakness Enumeration category CWE-121, which specifically addresses stack-based buffer overflow conditions, and represents a direct violation of secure coding practices regarding input validation and memory boundary checking. The flaw demonstrates a classic example of insufficient boundary checking where integer values are used directly in memory operations without proper range validation.
The operational impact of CVE-2016-10091 extends beyond simple denial-of-service conditions to potentially enable more sophisticated attack vectors. While the primary effect manifests as denial-of-service through application crashes and process termination, the underlying buffer overflow condition creates opportunities for attackers to execute arbitrary code on affected systems. The vulnerability affects any system running unrtf 0.21.9 or earlier versions that processes untrusted RTF documents, making it particularly dangerous in environments where document processing is automated or where users can upload or receive RTF files from untrusted sources. The attack surface is broad given RTF's widespread use in office applications, email clients, and document management systems, potentially allowing attackers to compromise systems through social engineering campaigns targeting document attachments.
Mitigation strategies for this vulnerability should focus on immediate software updates and input validation enhancements. The most effective remediation involves upgrading to a patched version of unrtf that addresses the integer validation issues in the affected command processing functions. Organizations should implement comprehensive input sanitization measures that validate all integer parameters before they are used in memory operations, particularly ensuring that negative values are rejected or properly converted to safe positive values. Network security controls including content filtering and sandboxing mechanisms can provide additional defense-in-depth layers to prevent malicious RTF documents from reaching vulnerable systems. The vulnerability also aligns with ATT&CK technique T1203, which describes the exploitation of software vulnerabilities for privilege escalation and system compromise, emphasizing the importance of timely patch management and vulnerability remediation across enterprise environments to prevent exploitation through this and similar buffer overflow conditions.