CVE-2026-49253

electerm has Path Traversal in Zmodem and Trzsz Download Filename Handling

Workarounds

If upgrading is not immediately possible, users can mitigate this vulnerability by:

1. Only connecting to trusted SSH servers
2. Rejecting or canceling any incoming Zmodem or Trzsz file transfers from untrusted sources
3. Avoiding the use of Zmodem (sz/rz) and Trzsz (trz/tsz) commands on untrusted servers

A path traversal vulnerability exists in the Zmodem and Trzsz file download handlers in electerm. When receiving files via Zmodem or Trzsz protocols, electerm uses the remote-supplied filename directly in path.join() with the user-selected download directory without sanitization.

A malicious SSH server or remote shell process can send a specially crafted filename such as ../escaped.txt to escape the user-selected download directory and write files to arbitrary locations on the user's filesystem, subject to process permissions.

Attack scenario:

1. User connects to a malicious SSH server
2. Attacker initiates a Zmodem or Trzsz file transfer
3. Attacker supplies a traversal filename (e.g., ../../.bashrc, ../escaped.txt)
4. User accepts the transfer and selects a download directory
5. File is written outside the selected directory, potentially overwriting sensitive files

Affected components:

• src/app/server/zmodem.js - prepareReceiveFile() at line 736
• src/app/server/trzsz.js - getUniqueFilePath() at line 559, openSaveFile() callback, and savedFilePaths mapping

Input manipulates file paths to reach files outside the intended directory, such as configuration or credential files. Typical impact: unauthorized file read or write outside the intended directory.

CVE-2026-49253 has a CVSS score of 7.1 (High). The vector is network-reachable, no privileges required, and user interaction required. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (3.11.11); upgrading removes the vulnerable code path.

Kodem intelligence

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• https://github.com/electerm/electerm/commit/fde153d677a170c5816368f6586647f3af4ef284

1. What is CVE-2026-49253? CVE-2026-49253 is a high-severity path traversal vulnerability in electerm (npm), affecting versions <= 3.11.0. It is fixed in 3.11.11. Input manipulates file paths to reach files outside the intended directory, such as configuration or credential files.
2. How severe is CVE-2026-49253? CVE-2026-49253 has a CVSS score of 7.1 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of electerm are affected by CVE-2026-49253? electerm (npm) versions <= 3.11.0 is affected.
4. Is there a fix for CVE-2026-49253? Yes. CVE-2026-49253 is fixed in 3.11.11. Upgrade to this version or later.
5. Is CVE-2026-49253 exploitable, and should I be worried? Whether CVE-2026-49253 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-49253 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-49253? Upgrade electerm to 3.11.11 or later.

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