# CVE-2026-121751: nvm evaluates a malicious mirror's index.tab version strings as shell arithmetic via stored LTS aliases

Status: published. Published: 2026-11-04. Updated: 2026-11-09.

Node Version Manager (nvm) is a POSIX-compliant shell function for managing multiple node.js versions. In versions 0.39.6 through 0.40.8, `nvm ls-remote` (and other commands that refresh remote LTS aliases) store the version column of the mirror's `index.tab` in `$NVM_DIR/alias/lts/` without validating it, and `nvm_normalize_lts` later evaluates any suffix of an `lts/-N` value inside shell arithmetic `$((N+1))`. Under bash and zsh, arithmetic evaluation expands command substitutions in array subscripts, so a stored value such as `lts/-10*path[$(cmd)1]` runs `cmd` as the user when the alias is later resolved by purely local commands (`nvm ls`, `nvm alias`, `nvm use --lts`, `nvm which lts/`), and in every new shell when the `default` alias is `lts/*`. Exploitation requires the victim to use a hostile mirror -- via a compromised mirror or CDN, a network man-in-the-middle of an `http://` mirror, or a maliciously configured `NVM_NODEJS_ORG_MIRROR` -- and to run an affected command. The same sink is also reachable from a project `.nvmrc`, which is treated as hardening. dash is not affected. Version 0.41.0 only passes an all-digit `lts/-N` offset to arithmetic and drops `index.tab` rows whose version is not a valid version string.

## Remediation

- fix: Upgrade to nvm 0.41.0 or later, which only lets an all-digit `lts/-N` offset reach shell arithmetic and drops mirror rows with invalid version strings. (Only needed if using a non-default mirror whose metadata contents you do not trust, or running nvm in untrusted project directories.) (source: CNA: harborist)
- workaround: Until upgrading, only run `nvm ls-remote` and LTS-refreshing commands against trusted mirrors over TLS, ensure `NVM_NODEJS_ORG_MIRROR` points only at a trusted endpoint, and do not run nvm in untrusted project directories. (source: CNA: harborist)
- fix: The reporting source identifies this reference as a patch. Check the advisory for affected versions and supported release branches. (source: CNA: harborist) — https://github.com/nvm-sh/nvm/commit/aa0572b7c48b2652a9f86276bbbf3840939981af
- fix: nvm-sh/nvm (other): GitHub reports patched versions 0.41.0. Check the advisory for the affected release branch. (source: GitHub GHSA-7prg-rw9c-82h7) — https://github.com/nvm-sh/nvm/security/advisories/GHSA-7prg-rw9c-82h7

## Affected products and versions

- nvm-sh / nvm: ≥ 0.39.6; < 0.41.0 (affected, semver). Source: CNA: harborist
-  / nvm-sh/nvm (nvm-sh/nvm): >= 0.39.6, <= 0.40.8 (affected, GitHub advisory range). Source: GitHub GHSA-7prg-rw9c-82h7

## Severity and prioritization

- CVSS 4.0: 2.1 (low); CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:A/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N; source: CNA: harborist

- CVSS 3.1: 3.1 (low); CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:N/I:L/A:N; source: CNA: harborist

- CVSS 4.0: 2.1 (low); CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:A/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X; source: NVD: 7ffcee3d-2c14-4c3e-b844-86c6a321a158

- CVSS 3.1: 3.1 (low); CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:N/I:L/A:N; source: NVD: 7ffcee3d-2c14-4c3e-b844-86c6a321a158

- CISA KEV: No listing in collected sources

- EPSS: 0.23% as of 2026-11-09; percentile 14.11%

- SSVC: exploitation none; automatable no; technical impact partial; source ADP: CISA-ADP

- Weaknesses: CWE-78, CWE-20

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://github.com/nvm-sh/nvm/security/advisories/GHSA-7prg-rw9c-82h7 (CNA: harborist; vendor-advisory)

- https://github.com/nvm-sh/nvm/commit/aa0572b7c48b2652a9f86276bbbf3840939981af (CNA: harborist; patch)

- https://github.com/nvm-sh/nvm/commit/aa0572b7c48b2652a9f86276bbbf3840939981af (7ffcee3d-2c14-4c3e-b844-86c6a321a158)

- https://github.com/nvm-sh/nvm/security/advisories/GHSA-7prg-rw9c-82h7 (7ffcee3d-2c14-4c3e-b844-86c6a321a158)

- https://github.com/nvm-sh/nvm/security/advisories/GHSA-7prg-rw9c-82h7 (GitHub Security Advisories; advisory)

## Provenance

- CNA: harborist: https://www.cve.org/CVERecord?id=CVE-2026-121751; retrieved 2026-11-09; source updated 2026-11-09

- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-121751; retrieved 2026-11-05; source updated 2026-11-04

- GitHub Security Advisories: https://github.com/nvm-sh/nvm/security/advisories/GHSA-7prg-rw9c-82h7; retrieved 2026-11-06; source updated 2026-11-04

- FIRST EPSS: https://api.first.org/data/v1/epss?cve=CVE-2026-121751; retrieved 2026-11-09; source updated Not reported

Revision: 3b906d3bf48bce2d74dca5f14a471ad6cb4d4758c5220c433100344b82d501e8

Canonical: https://y2.dev/cve/CVE-2026-121751

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