Summary
virtualenv writes prompt values into pyvenv.cfg without sanitizing line boundaries, allowing configuration injection
pyvenv.cfg is a line-based format with no escape syntax. PyEnvCfg.write() wrote values verbatim, while PyEnvCfg._read_values() parses the file with str.splitlines(). A value containing a line boundary therefore became additional configuration lines, and because reading is last-wins, the injected keys replaced any key written earlier in the file.
Details
The boundary set is the one str.splitlines() recognizes, which is wider than \n: \r, \v, \f, the file, group and record separators, U+0085, U+2028 and U+2029 were all written through unchanged and all split the line when read back.
Workarounds
Do not pass externally influenced data as the virtualenv prompt. Strip line boundaries from any value before using it as --prompt or VIRTUALENV_PROMPT.
Impact
The prompt value is the reachable input: it is set by --prompt, by the VIRTUALENV_PROMPT environment variable, or from the config file, and write() emits prompt before home. A crafted prompt can therefore set home in the generated pyvenv.cfg:
$ virtualenv --prompt $'x"\nhome = /attacker/path\nprompt = "z' venv
$ grep '^home' venv/pyvenv.cfg
home = /attacker/path
home is what tooling reads to locate the base interpreter, so a consumer that trusts it can be pointed elsewhere. implementation, version_info, version, executable, command and virtualenv are also written before prompt and can be replaced the same way.
This requires the prompt to come from somewhere other than the person running the command, for example a CI job templating a branch name into it, tooling deriving an environment name from user-supplied data, or an inherited VIRTUALENV_PROMPT. Where the operator supplies the prompt directly they already control the command line, and the effect is corruption rather than privilege gain: the value is truncated at the boundary and read back with a dangling quote.
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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PyEnvCfg.write() now collapses those boundaries to spaces as it serializes each line, so it cannot emit a structurally invalid file regardless of what a caller places in content.
Frequently Asked Questions
- What is CVE-2026-102938? CVE-2026-102938 is a medium-severity security vulnerability in virtualenv (pip), affecting versions <= 21.7.10. It is fixed in 21.7.11.
- Which versions of virtualenv are affected by CVE-2026-102938? virtualenv (pip) versions <= 21.7.10 is affected.
- Is there a fix for CVE-2026-102938? Yes. CVE-2026-102938 is fixed in 21.7.11. Upgrade to this version or later.
- Is CVE-2026-102938 exploitable, and should I be worried? Whether CVE-2026-102938 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-2026-102938 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-2026-102938? Upgrade
virtualenvto 21.7.11 or later.