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VulnerabilityPublished

CVE-2026-102938: pypa virtualenv · CRLF Injection

Affects pypa virtualenvSource CVE Database V5

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Not known to be exploited · CVSS 5.8 Medium : upgrade to 21.7.11 when convenient.

Data as of 12 Nov 2026, 23:24 UTC

CVSS 4.0 base score
5.8Medium
How severe the flaw is on the 0–10 CVSS scale.
EPSS
0.1% chance of exploitation in 30 days – higher than 3% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch
Available – fixed in 21.7.11
CVSS:4.0/AV:L/AC:L/AT:P/PR:N/UI:P/VC:L/VI:H/VA:L/SC:N/SI:N/SA:N

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 29 Sep 2026

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponized: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq Mirage: no evidence on record.

    No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 13 Nov 2026.

What to do

Upgrade pypa virtualenv to 21.7.11.

Affected software

ProductAffectedFixed in
pypavirtualenvAffected
  • <21.7.11
Fixed in
  • 21.7.11
PyPIvirtualenvpkg:pypi/virtualenvOther threatsAffected
  • <21.7.11
Fixed in
  • 21.7.11

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

A patch is available in virtualenv version 21.7.11 and later that collapses line boundary characters to spaces during serialization, preventing injection of additional configuration lines. Users should upgrade to version 21.7.11 or later. As a workaround, do not pass externally influenced data as the virtualenv prompt. Strip line boundary characters from any value before using it as --prompt or in the VIRTUALENV_PROMPT environment variable.

Description

### Summary `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. ### 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`: ```console $ 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. ### 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. ### Patches `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`. ### 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`.

References

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