Summary
virtualenv activation scripts run code from a path that contains a placeholder name
Workarounds
Do not create an environment whose path or --prompt contains a placeholder name such as __VIRTUAL_NAME__, __VIRTUAL_ENV__ or __VIRTUAL_PROMPT__, and inspect the generated activation script before you source one you did not create.
Credits
Kevin Stubbings (@Kwstubbs) of GitHub Security Lab reported this issue.
Impact
ViaTemplateActivator.instantiate_template replaces the placeholders in an activation template one key at a time, each across the whole text. When a value that it already substituted and quoted contains the name of a later placeholder, the later pass rewrites that name inside the quoted literal. The inserted value brings its own quotes, which close the outer literal, and the rest of the path runs as code when a user activates the environment.
__VIRTUAL_NAME__ holds the environment's directory name, so a destination such as A__VIRTUAL_NAME__B/x'$(touch PWNED)'y is enough. In the default activate for bash, the VIRTUAL_ENV line renders as:
VIRTUAL_ENV='/tmp/t/A'x'"'"'$(touch PWNED)'"'"'y'B/x'"'"'$(touch PWNED)'"'"'y'
Sourcing that script runs touch PWNED. The same payload in a path without the placeholder name runs nothing. activate.fish runs the command the same way, and the reporter also showed Python code execution through activate.xsh and bin/activate_this.py. In activate.csh, a directory named after a prompt display placeholder, such as __VIRTUAL_PROMPT_DISPLAY_TCSH__, breaks the script with Unmatched '''.
No change to quote() can stop this, because the rewrite happens after quote() ran; it defeats shlex.quote and repr() alike.
An attacker needs to influence the destination path or --prompt: a CI job or wrapper tool that builds the path from a branch or project name, or a directory in a cloned repository or unpacked archive.
The bug affects versions 20.26.6 through 21.14.1. Version 20.26.6 first quoted template values (#2768) and introduced the per-key loop.
Untrusted input reaches a shell command, allowing arbitrary commands to run on the host. Typical impact: code execution in the application's environment.
CVE-2026-113776 has a CVSS score of 7.8 (High). The vector is requires local access, 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 (21.14.2); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
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. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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Fixed in 21.14.2. Activation scripts now keep a placeholder name in the environment's path or prompt as plain text, and activating the example above runs nothing. Fix: https://github.com/pypa/virtualenv/commit/602b26623a724827ff171bf11fef4ad186d01f74
Frequently Asked Questions
- What is CVE-2026-113776? CVE-2026-113776 is a high-severity OS command injection vulnerability in virtualenv (pip), affecting versions >= 20.26.6, <= 21.14.1. It is fixed in 21.14.2. Untrusted input reaches a shell command, allowing arbitrary commands to run on the host.
- How severe is CVE-2026-113776? CVE-2026-113776 has a CVSS score of 7.8 (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.
- Which versions of virtualenv are affected by CVE-2026-113776? virtualenv (pip) versions >= 20.26.6, <= 21.14.1 is affected.
- Is there a fix for CVE-2026-113776? Yes. CVE-2026-113776 is fixed in 21.14.2. Upgrade to this version or later.
- Is CVE-2026-113776 exploitable, and should I be worried? Whether CVE-2026-113776 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
- What actually determines whether CVE-2026-113776 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.
- How do I fix CVE-2026-113776? Upgrade
virtualenvto 21.14.2 or later.