How severe is CVE-2026-113726?

CVE-2026-113726 has a CVSS score of 7.8/10, rated HIGH. Immediate patching is strongly recommended.

Which packages are affected by CVE-2026-113726?

CVE-2026-113726 affects the following packages: virtualenv (PyPI). Ecosystems affected: PyPI.

How do I fix CVE-2026-113726?

Update virtualenv to 21.14.4 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-113726 is resolved across your whole dependency graph.

How do I detect CVE-2026-113726 in my PyPI dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for virtualenv, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2026-113726 if there is no patch (or I can't update yet)?

Stop passing untrusted input into the interpreter or shell: call the affected binary with an argument array rather than a composed command string, reject anything outside a strict allowlist of expected values, and run the component under an account that cannot reach beyond the work it legitimately does.

Is CVE-2026-113726 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-113726 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2026-113726?

CVE-2026-113726 has an EPSS (Exploit Prediction Scoring System) score of 0.2%, placing it in the 14th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2026-113726?

CVE-2026-113726 is classified as OS Command Injection (CWE-78), CWE-116 (CWE-116). These weakness types describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation. This is a high-impact weakness class that often enables remote code execution or data exposure.

When was CVE-2026-113726 published, and has it been updated?

CVE-2026-113726 was published on October 20, 2026 and was last updated on October 24, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🐍

🐍 PyPI

Not in CISA KEV

HIGH severity

CVE-2026-113726 — virtualenv

HIGHFix: pypa/virtualenv@5b91536

CVE-2026-113726 is a high-severity (CVSS 7.8) OS Command Injection vulnerability in virtualenv. A fix is available for virtualenv — see the affected versions and patch details below.

virtualenv activate runs commands from the environment name in zsh with PROMPT_SUBST

Also known asGHSA-5vjq-rrrf-7h2q

Published

Oct 20, 2026

Updated

Oct 24, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Oct 23, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗

0.2%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs14th percentile — riskier than 14% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

CVE-2026-113726 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.

Where this sits among everything scored

Of 394,415 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.

Real-World Exposure

1 pkg affected

🐍virtualenv

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.

Description

Impact

zsh users activate an environment with the bash activate script, which puts the environment name into PS1. Since 21.13.0 the script escapes backslashes, dollar signs and backticks in that name, but only when BASH_VERSION is set, so zsh gets the raw value. With the PROMPT_SUBST option set, zsh runs parameter expansion, command substitution and arithmetic expansion on PS1 each time it draws the prompt. A name that contains $(...), backticks or ${...} then runs as commands in the user's shell, once per prompt.

The name comes from the environment directory, or from --prompt or VIRTUALENV_PROMPT. After you create an environment with:

$ virtualenv 'x$(touch PWNED)y'

source 'x$(touch PWNED)y/bin/activate' in a zsh session with PROMPT_SUBST set creates PWNED, and the prompt shows (xy). Passing that value as --prompt to an environment with a plain name has the same effect. Without PROMPT_SUBST, zsh shows the name as text and runs nothing. bash runs nothing either.

A plain zsh starts with PROMPT_SUBST off. oh-my-zsh users have it on: oh-my-zsh loads lib/theme-and-appearance.zsh at startup, and that file sets it. An attacker needs to influence the environment path or prompt: a CI job or wrapper tool that passes a branch, project or job name through, or a directory in a cloned repository or unpacked archive. --prompt . takes the current directory's name.

zsh also reads % in PS1 as a prompt escape, so a name with %n showed the user name in place of those characters, though without running commands.

The bug is in releases up to and including 21.14.3. The payload runs on 20.26.6 and 21.14.3, and the reporter confirmed 21.9.1.

Patches

Fixed in 21.14.4. Under zsh, activate now escapes the name the way it does under bash and doubles %, so the example above runs nothing and the prompt shows the name as given. zsh gets the escaping even when PROMPT_SUBST is off, because a user can set the option after activation; a name with a backslash, dollar sign or backtick then shows the added backslashes. Fix: https://github.com/pypa/virtualenv/commit/5b915367da82bd024b2a0d28d2f98007034b4aa2

Workarounds

Set VIRTUAL_ENV_DISABLE_PROMPT=1 before you source activate, which leaves PS1 alone, or run unsetopt prompt_subst if your prompt does not need it. Check the name of an environment you did not create before you source its activate.

Credits

Kaya Emre Arikan (@kemrec) reported this issue.

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
🐍PyPI	`virtualenv`	all versions	21.14.4`pip install --upgrade 'virtualenv==21.14.4'`

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for virtualenv, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update virtualenv to 21.14.4 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-113726 is resolved across your whole dependency graph.
Workarounds
Stop passing untrusted input into the interpreter or shell: call the affected binary with an argument array rather than a composed command string, reject anything outside a strict allowlist of expected values, and run the component under an account that cannot reach beyond the work it legitimately does.

Frequently Asked Questions

### Impact zsh users activate an environment with the bash `activate` script, which puts the environment name into `PS1`. Since 21.13.0 the script escapes backslashes, dollar signs and backticks in that name, but only when `BASH_VERSION` is set, so zsh gets the raw value. With the `PROMPT_SUBST` option set, zsh runs parameter expansion, command substitution and arithmetic expansion on `PS1` each time it draws the prompt. A name that contains `$(...)`, backticks or `${...}` then runs as commands in the user's shell, once per prompt. The name comes from the environment directory, or from `--pr