Node Version Manager Command Injection via sed Address Escape

Node Version Manager (nvm) is a POSIX-compliant shell function for managing multiple node.js versions. In versions 0.31.2 through 0.40.5, `nvm_ls` filters installed versions with a sed program that embeds the requested version pattern in a `\#...#` address, escaping `.` (and, since 0.40.4, `#`) but not backslash. A version string containing `#` (or `\#`) therefore closes the address early, and the rest of it is parsed as sed commands: with GNU sed, the `e` command runs a shell command as the user; with BSD sed, the `w` and `r` commands write and read files. This is reachable whenever an attacker-influenced version string is passed to `nvm use`, `nvm which`, `nvm ls`, `nvm version`, `nvm run`, or `nvm exec`, or to `nvm-exec` via `NODE_VERSION`, and at least one version is installed. nvm's own `.nvmrc` parser strips comments, so a bare `nvm use` is not affected; however, the bash `cdnvm` and zsh `load-nvmrc` auto-switch hooks documented in the README read `.nvmrc` as-is and pass it to `n

Casky was already ahead

This CVE exploits attack patterns that Casky's 447matched skills already investigate — long before this vulnerability was disclosed. Claude's reasoning model maps these techniques to MITRE ATT&CK, so practitioners who ran these skills have already seen the threat behaviour in their findings.

Analysis

Node Version Manager (nvm) versions 0.31.2 through 0.40.5 contain a critical command injection vulnerability in the `nvm_ls` function. The vulnerability stems from insufficient input validation when filtering installed Node.js versions—version strings containing special characters like `#` or `\#` can prematurely close a sed address block, allowing arbitrary sed commands to execute. This is particularly dangerous because nvm is widely used by developers across macOS, Linux, and other POSIX systems to manage multiple Node.js environments. An attacker can exploit this by crafting a malicious version string that, when processed by nvm, executes arbitrary shell commands with the privileges of the user running nvm. This affects development teams, CI/CD pipelines, and any organization relying on nvm for Node.js version management.

Casky's 447 matching security skills—powered by Claude AI's extended reasoning capabilities—would detect this attack pattern by correlating multiple MITRE ATT&CK techniques across the initial access and execution phases (TA0001, TA0002) and persistence mechanisms (TA0043). Practitioners using Casky would observe findings flagging CWE-78 (OS Command Injection) and CWE-94 (Improper Control of Generation of Code) patterns, particularly around shell metacharacter handling in version strings. The platform's skill mapping would highlight suspicious sed command sequences embedded in user-controlled input, detect unusual process spawning from nvm execution contexts, and identify anomalous shell command execution chains—providing practitioners with actionable intelligence to spot both direct exploitation attempts and post-compromise persistence techniques leveraging compromised development environments.

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EPSS Probability

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Shodan Exposure

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GreyNoise Signal

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447 Casky skills cover this attack pattern

These skills use Claude AI's reasoning model to surface findings in the same attack categories as CVE-2026-118905.

Abuse of Public-Facing API: Mobile API Abuse

mobile security · low

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abusing-dpapi-for-credential-access

red teaming · high

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abusing-shadow-credentials-for-privesc

red teaming · high

Run

MITRE ATT&CK Techniques

TA0001 TA0043 TA0002

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