CVE-2026-58317
Received Received - Intake

Unsigned to Signed Conversion Error in Tera Term TTSSH2 Plugin

Publication date: 2026-07-17

Last updated on: 2026-07-17

Assigner: JPCERT/CC

Description
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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Meta Information

Published
2026-07-17
Last Modified
2026-07-17
Generated
2026-07-17
AI Q&A
2026-07-17
EPSS Evaluated
N/A
NVD
CVE-2026-58317
EUVD
EUVD-2026-45140

Affected Vendors & Products

Showing 4 associated CPEs
Vendor Product Version / Range
teraterm_project ttssh2 From 1.00_alpha1 (inc) to 3.6.1 (inc)
teraterm_project tera_term From 2.05 (inc) to 5.6.1 (inc)
teraterm_project ttssh2 3.6.2
teraterm_project tera_term 5.6.2

Helpful Resources

Exploitability

CWE
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KEV
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CWE ID Description
CWE-196 The product uses an unsigned primitive and performs a cast to a signed primitive, which can produce an unexpected value if the value of the unsigned primitive can not be represented using a signed primitive.

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Executive Summary

CVE-2026-58317 is an Unsigned to Signed Conversion Error (CWE-196) in the TTSSH2 plugin of Tera Term. When Tera Term tries to connect to a malicious server, crafted packets can cause out-of-bounds memory reads or writes. This may expose adjacent memory data or lead to crashes in Tera Term.

Detection Guidance

This vulnerability affects TTSSH2 versions 3.6.1 and earlier. To detect it, check the installed version of Tera Term or TTSSH2 on your system. For Windows systems, look in the installed programs list or check the version in the Tera Term installation directory. Command to check version: 'ttssh2 -v' or inspect the file properties of ttssh2.dll.

Impact Analysis

An attacker could exploit this to cause Tera Term to crash or behave unexpectedly. Sensitive data in adjacent memory might be exposed during SSH connections. The impact is limited to temporary null-byte writes, but could still disrupt normal operations.

Compliance Impact

This vulnerability may lead to unintended data exposure or crashes in Tera Term, which could result in unauthorized access to sensitive information during SSH connections. This could potentially violate compliance requirements under GDPR (data protection) or HIPAA (healthcare data security) if sensitive data is exposed or mishandled due to the flaw.

Mitigation Strategies

Upgrade to TTSSH2 version 3.6.2 or later, which is included in Tera Term 5.6.2. Since no fixes are planned for Tera Term 4.x, users should migrate to the latest 5.x version. Ensure all systems using Tera Term for SSH connections are updated immediately to prevent potential out-of-bounds memory access.

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