CVE-2026-103678 in tnef
Summary
by MITRE • 10/01/2026
A flaw was found in tnef. An attacker can exploit this vulnerability by providing a specially crafted file containing uncompressed Rich Text Format (RTF) data. Because the application fails to properly validate input buffer boundaries before copying data in get_rtf_data_from_buf(), reading beyond the allocated memory occurs. This flaw can cause the application to crash, leading to a Denial of Service (DoS), or leak sensitive memory contents into extracted output files.
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Analysis
by VulDB Data Team • 10/01/2026
The vulnerability identified within the tnef utility represents a critical input validation failure that compromises both the availability and confidentiality of systems processing Microsoft Outlook Rich Text Format attachments. This flaw is rooted in the get_rtf_data_from_buf function, which is responsible for extracting uncompressed RTF data from TNEF containers. The core technical deficiency lies in the absence of rigorous boundary checks before memory copy operations are executed. When an attacker supplies a specially crafted file containing malformed or oversized RTF payloads, the application fails to verify that the source buffer size aligns with the destination allocation limits. This lack of validation allows for out-of-bounds reads, where the program accesses memory locations beyond the originally allocated buffer space. Such behavior is classically categorized under CWE-126, which denotes Buffer Over-read vulnerabilities, and often intersects with CWE-20 regarding improper input validation mechanisms that fail to constrain data within expected parameters.
The operational impact of this vulnerability manifests primarily through two distinct attack vectors: denial of service and information disclosure. In the context of availability, triggering the out-of-bounds read can cause immediate application instability or crashes. For services relying on tnef for automated email attachment processing, such as mail gateways or document management systems, a single crafted file can disrupt operations by crashing the parsing process. This aligns with ATT&CK technique T1499, Endpoint Denial of Service, where an adversary leverages software flaws to degrade system performance or render resources unavailable. The crash results from undefined behavior in memory handling, potentially leading to segmentation faults or other fatal errors that halt normal execution flow and require manual intervention or service restarts to restore functionality.
Beyond availability concerns, the vulnerability poses a severe risk to data confidentiality due to its potential for sensitive information leakage. When the application reads beyond allocated buffer boundaries, it inadvertently accesses adjacent memory regions containing residual data from previous operations. This uncontrolled access can result in the inclusion of private keys, session tokens, passwords, or other proprietary data into the extracted output files. An attacker who controls the input file and has access to the resulting outputs could harvest this leaked information for further exploitation. This scenario corresponds to CWE-200, Exposure of Sensitive Information to an Unauthorized Actor, highlighting how improper memory management directly facilitates unauthorized data retrieval without requiring direct system compromise or privilege escalation.
Mitigation strategies must focus on both immediate remediation and long-term defensive coding practices. The primary solution involves applying vendor-provided patches that update the tnef package with corrected source code implementing strict boundary checks in the get_rtf_data_from_buf function. Developers should ensure that all buffer copy operations are preceded by explicit size validations to guarantee that read limits do not exceed allocated memory regions. In environments where immediate patching is not feasible, organizations can implement input filtering at network or application layers to detect and block malformed TNEF files before they reach the vulnerable component. Additionally, enabling core dump analysis capabilities can aid in forensic investigations if an exploitation attempt occurs, allowing security teams to assess the extent of memory exposure and adjust monitoring rules accordingly. Regular code audits focusing on CWE-126 patterns are essential for preventing similar vulnerabilities in future software updates.