CVE-2026-58317 in Tera Term
Summary
by MITRE • 07/17/2026
Unsigned to Signed Conversion Error (CWE-196) vulnerability exists in TTSSH2 plugin of Tera Term provided by TeraTerm Project. When Tera Term attempts to establish an SSH connection to a server set up by an attacker, out-of-bounds read/write may occur. As a result, the contents of adjacent memory regions may be transmitted to the server, and Tera Term may behave unexpected or terminate abnormally.
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Analysis
by VulDB Data Team • 07/17/2026
The vulnerability described represents a critical unsigned to signed conversion error that manifests within the TTSSH2 plugin of Tera Term software developed by the TeraTerm Project. This class of vulnerability falls under CWE-196 which specifically addresses issues arising from improper handling of data type conversions between unsigned and signed integer representations. The flaw occurs during SSH connection establishment processes when Tera Term interacts with maliciously configured servers, creating a pathway for potentially dangerous memory access patterns.
The technical implementation of this vulnerability stems from how the TTSSH2 plugin processes certain numerical values during the SSH handshake protocol execution. When unsigned integers are converted to signed integers without proper bounds checking or validation, the conversion can result in unexpected behavior that manifests as out-of-bounds read/write operations. This type of error commonly occurs in cryptographic implementations where packet sizes, sequence numbers, or other numeric fields may exceed the representable range of signed integer types, particularly when dealing with network protocol parsing.
The operational impact of this vulnerability extends beyond simple application instability to potentially expose sensitive information through memory disclosure attacks. When out-of-bounds memory reads occur, adjacent memory regions containing potentially confidential data such as session tokens, cryptographic keys, or other sensitive information may be inadvertently transmitted to the attacker-controlled server. This creates a significant risk for environments where Tera Term is used for remote administration or secure communications, as it could lead to credential theft, session hijacking, or exposure of proprietary data stored in memory.
The behavior disruption caused by this vulnerability can result in application crashes, unexpected termination, or denial of service conditions that affect legitimate users attempting to establish secure connections. From an attacker perspective, this vulnerability provides a means to exploit the software's handling of numeric conversions to gain information about the target system's memory layout or extract valuable data through carefully crafted malicious server responses. The vulnerability demonstrates poor input validation practices and highlights the importance of proper type safety in security-critical applications.
Mitigation strategies should focus on implementing comprehensive bounds checking for all integer conversions, particularly when dealing with network protocol data that may be manipulated by attackers. Security updates should ensure proper handling of unsigned to signed conversions through explicit type casting with appropriate range validation. The recommended approach involves applying the principle of least privilege in memory access patterns and ensuring that all numeric operations maintain integrity throughout the conversion process. Additionally, implementing address space layout randomization and stack canaries can provide additional defense-in-depth measures against potential exploitation attempts.
This vulnerability aligns with ATT&CK technique T1059 which covers command and scripting interpreter usage, as attackers may leverage such memory corruption flaws to execute malicious code or gain unauthorized access to systems. The CWE-196 classification indicates that this represents a fundamental software design flaw that requires careful attention during development phases to prevent similar issues in other components of the Tera Term suite or related applications. Organizations should prioritize patching affected versions and consider implementing network monitoring to detect unusual data transmission patterns that may indicate exploitation attempts targeting this specific vulnerability.