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Response snapshot Oct 26, 2026, 22:06 UTC

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VulnerabilityCVE-2026-115586

virtualenv: Bash activator leaves the --prompt value unescaped in PS1 when promptvars is off, so prompt expansion later executes it (regression in 21.14.9)

The bash activator puts the caller-supplied prompt value into `PS1` unescaped whenever `promptvars` is off at activation time, and assumes prompt expansion can never run afterwards.

Published Updated

At a glance

Exploited
Not known
Severity
7.1 High (CVSS 4.0)
Chance of exploitation
0.2% in the next 30 days
Sources
2 independent sources

What to do

GitHub lists first patched versions: virtualenv: 21.14.13. Confirm the affected range and upgrade guidance in the exact advisory.

Read GitHub-reviewed advisory GHSA-cx6f-vjhg-g3cc (opens a new tab)

What happened

## Summary

The bash activator puts the caller-supplied prompt value into `PS1` unescaped whenever `promptvars` is off at activation time, and assumes prompt expansion can never run afterwards.

`promptvars` and posix mode are runtime shell state, not a property of the activation moment: re-enabling prompt expansion in the same shell (`shopt -s promptvars`, `set -o posix`) or starting an interactive child bash that inherits the exported `PS1` makes bash expand the stored value and run the command substitution in it.

An attacker who controls the prompt value gets command execution as the user who sources `bin/activate`.

Continue reading

This is a regression. 21.14.8 escaped `$` and the backtick unconditionally and stays inert under the same sequence. The 21.14.9 fix for GHSA-6w3r-xr62-4xcp (#3418) rewrote that block and left bash with a path that stores the raw value whenever `promptvars` is off.

## Affected area

Activation scripts (activate, activate.bat, activate.csh, activate.fish, activate.nu, Activate.ps1, activate.xsh) — specifically the bash `bin/activate`.

## Attacker-controlled input

The `--prompt` value, which the security policy already lists as a value that may come from project metadata the user did not write. It reaches `virtualenv` as `--prompt` on the command line or as the `prompt` argument of the API, is written into `bin/activate` as the literal `VIRTUAL_ENV_PROMPT` assignment (correctly quoted, the value arrives there as data), and the script then copies it into `PS1` without escaping `$` or the backtick.

Example: a repository or tool config supplies a prompt such as `x$(id > /tmp/ve-pwn)y`; the victim creates and later activates the environment.

## Details

Source of the latest release: [`src/virtualenv/activation/bash/activate.sh` lines 140-160](https://github.com/pypa/virtualenv/blob/21.14.12/src/virtualenv/activation/bash/activate.sh#L140-L160)

```sh if [ -z "${VIRTUAL_ENV_DISABLE_PROMPT-}" ] && { [ -n "${BASH_VERSION-}" ] || [ -n "${ZSH_VERSION-}" ]; }; then _OLD_VIRTUAL_PS1="${PS1-}" # bash expands PS1 after decoding its prompt escapes when promptvars is on or in posix mode, so the prompt holds a # reference to the variable and its value never reaches that expansion; otherwise only the decode runs and # backslashes need doubling.

if [ -n "${BASH_VERSION-}" ] && { shopt -q promptvars || shopt -qo posix; }; then PS1='(${VIRTUAL_ENV_PROMPT-}) '"${PS1-}" else _VIRTUAL_PROMPT="${VIRTUAL_ENV_PROMPT//\\/\\\\}" if [ -n "${ZSH_VERSION-}" ]; then _VIRTUAL_PROMPT="${_VIRTUAL_PROMPT//\$/\\\$}" _VIRTUAL_PROMPT="${_VIRTUAL_PROMPT//\`/\\\`}" _VIRTUAL_PROMPT="${_VIRTUAL_PROMPT//\%/%%}" fi PS1="(${_VIRTUAL_PROMPT}) ${PS1-}" unset _VIRTUAL_PROMPT fi fi ```

Two separate mistakes combine:

1. A runtime shell option is treated as a constant. `shopt -u promptvars` at the moment of `source` does not bind the shell forever: `shopt -s promptvars` and `set -o posix` both re-enable PS1 expansion in the same shell. The code itself tests `shopt -qo posix` because posix mode expands the prompt regardless of `promptvars`, which shows the expansion state is not fixed by the activation. 2.

The escaping that would keep the value inert in that mode is missing for bash. GHSA-5vjq-rrrf-7h2q ("activate runs commands from the environment name in zsh with PROMPT_SUBST") fixed exactly this shape for zsh, reasoning that "a user can set it after activation", by escaping `$` and the backtick. Bash lost the equivalent escaping in the same commit that added the zsh branch.

The rendered prompt shows the regression directly:

``` 21.14.8 PS1 = (x\\$(id > /tmp/ve-pwn)y) /tmp/ve-pwn)y) /tmp/ve-pwn)y) /tmp/ve-pwn)y' /tmp/venv-demo

cat > /tmp/rc `\$`, backtick -> ``\` ``, `\` -> `\\`). Verified on bash 5.1.16 that a `PS1` built that way is inert with `promptvars` on, with `promptvars` off, and with `promptvars` off followed by posix mode, while still rendering the literal value on screen. That is better than both current shapes: 21.14.8's four-level escaping left stray backslashes on screen, which is why the block was rewritten.

```sh else _VIRTUAL_PROMPT="${VIRTUAL_ENV_PROMPT//\\/\\\\}" _VIRTUAL_PROMPT="${_VIRTUAL_PROMPT//\$/\\\$}" _VIRTUAL_PROMPT="${_VIRTUAL_PROMPT//\`/\\\`}" if [ -n "${ZSH_VERSION-}" ]; then _VIRTUAL_PROMPT="${_VIRTUAL_PROMPT//\%/%%}" fi PS1="(${_VIRTUAL_PROMPT}) ${PS1-}" ```

For the tests, `tests/unit/activation/test_bash.py::test_bash_prompt_options` already parametrises `("before", "after", "expected")` and covers `before="shopt -u promptvars"` with `after=""`. The missing axis is the transition: `("shopt -u promptvars", "shopt -s promptvars", ...)` and `("shopt -u promptvars", "set -o posix", ...)`, with the existing `PWNED` check asserting no file was created.

## Latest release

- [x] The problem reproduces on the latest virtualenv release.

Affected package ranges reported by GitHub: virtualenv: >= 21.14.9, < 21.14.13

Scores and how they were measured

CVSS base severity

7.1

Version 4.0As of

CVSS:4.0/AV:L/AC:H/AT:P/PR:N/UI:A/VC:H/VI:H/VA:H/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

Measurement source (opens a new tab)

How bad it is if exploited. Not a prediction of exploitation or proof you are exposed.

EPSS probability

0.2%

Scored Percentile 9.5%

Model and measurement source (opens a new tab)

A model's estimate of exploitation in the next 30 days, not certainty or your own risk.

Related technology

Sources

  1. Primary source

    GitHub-reviewed advisory GHSA-cx6f-vjhg-g3cc (opens a new tab)

    The public advisory supplies the description, affected package/version ranges, and any listed CVSS metric. GitHub review is not local review.

    Published Checked

  2. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-cx6f-vjhg-g3cc, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  3. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-cx6f-vjhg-g3cc, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  4. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-cx6f-vjhg-g3cc, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  5. Primary source

    NVD CVE-2026-115586 (opens a new tab)

    NVD record: description, CVSS (the CNA score is preferred), affected products, and publication date. Not evidence of exploitation.

    Published Checked

  6. Primary source

    NVD CVE API 2.0 (opens a new tab)

    The NVD API page that supplied this CVE record.

    Published Date not suppliedChecked

  7. Primary source

    NVD CVE API 2.0 (opens a new tab)

    The NVD API page that supplied this CVE record.

    Published Date not suppliedChecked

  8. Primary source

    NVD CVE API 2.0 (opens a new tab)

    The NVD API page that supplied this CVE record.

    Published Date not suppliedChecked

  9. Primary source

    FIRST measured EPSS score (opens a new tab)

    Measured EPSS probability and percentile for CVE-2026-115586, scored 2026-10-26. This is a model estimate, not proof of exposure.

    Published Checked

Cite this record

For factual claims, cite the primary sources above; cite KEVWire for its compilation, dates, and classifications.

APA

KEVWire. (2026, October 26). virtualenv: Bash activator leaves the --prompt value unescaped in PS1 when promptvars is off, so prompt expansion later executes it (regression in 21.14.9) (CVE-2026-115586). https://kevwire.com/record/CVE-2026-115586

MLA

"virtualenv: Bash activator leaves the --prompt value unescaped in PS1 when promptvars is off, so prompt expansion later executes it (regression in 21.14.9) (CVE-2026-115586)." KEVWire, 26 Oct. 2026, kevwire.com/record/CVE-2026-115586.

Chicago

KEVWire. "virtualenv: Bash activator leaves the --prompt value unescaped in PS1 when promptvars is off, so prompt expansion later executes it (regression in 21.14.9) (CVE-2026-115586)." Last modified October 26, 2026. https://kevwire.com/record/CVE-2026-115586.

Evidence summary (plain text)

virtualenv: Bash activator leaves the --prompt value unescaped in PS1 when promptvars is off, so prompt expansion later executes it (regression in 21.14.9) (Oct 23, 2026).
The bash activator puts the caller-supplied prompt value into `PS1` unescaped whenever `promptvars` is off at activation time, and assumes prompt expansion can never run afterwards. `promptvars` and posix mode are runtime shell state, not a property of the activation moment: re-enabling prompt expansion in the same shell (`shopt -s promptvars`, `set -o posix`) or starting an interactive child bash that inherits the exported `PS1` makes bash expand the stored value and run the command substitution in it. An attacker who controls the prompt value gets command execution as the user who sources `bin/activate`.

This is a regression. 21.14.8 escaped `$` and the backtick unconditionally and stays inert under the same sequence. The 21.14.9 fix for GHSA-6w3r-xr62-4xcp (#3418) rewrote that block and left bash with a path that stores the raw value whenever `promptvars` is off.
CVSS 7.1 (version 4.0; evidence as of Oct 26, 2026; https://nvd.nist.gov/vuln/detail/CVE-2026-115586).
EPSS 0.2% for the following 30 days, scored Oct 26, 2026 (https://api.first.org/data/v1/epss?cve=CVE-2026-115586&date=2026-10-26).
Sources:
GitHub-reviewed advisory GHSA-cx6f-vjhg-g3cc: https://github.com/advisories/GHSA-cx6f-vjhg-g3cc
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yM1QyMDo1MTozMFrOAAf0Mg%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yM1QyMDo0OToxMlrOAAf0LQ%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc
NVD CVE-2026-115586: https://nvd.nist.gov/vuln/detail/CVE-2026-115586
NVD CVE API 2.0: https://services.nvd.nist.gov/rest/json/cves/2.0?lastModStartDate=2026-10-26T13:11:54.490Z&lastModEndDate=2026-10-26T14:45:57.368Z&resultsPerPage=500&startIndex=0
NVD CVE API 2.0: https://services.nvd.nist.gov/rest/json/cves/2.0?lastModStartDate=2026-10-26T12:40:01.998Z&lastModEndDate=2026-10-26T14:10:55.205Z&resultsPerPage=500&startIndex=500
NVD CVE API 2.0: https://services.nvd.nist.gov/rest/json/cves/2.0?pubStartDate=2026-10-12T13:35:55.142Z&pubEndDate=2026-10-26T13:35:55.142Z&resultsPerPage=500&startIndex=9000
FIRST measured EPSS score: https://api.first.org/data/v1/epss?cve=CVE-2026-115586&date=2026-10-26
Record ID: CVE-2026-115586.
Record origin: Ingested record.
AI evidence: Not assessed.
Known exploitation: Not assessed.
Zero-day status: Not assessed. KEV membership alone does not establish zero-day status.
About this data

This record was ingested from a data source. Retrieved: Oct 26, 2026, 19:40 UTC. Ingestion is not an independent editorial investigation.

A CISA KEV listing documents known exploitation, not necessarily a zero-day; absence from the catalog does not prove a vulnerability has never been exploited.

Technology tags indicate possible relevance, not verified exposure. Confirm the affected product, version, and configuration against your own inventory; KEVWire does not scan your systems.

A personal reading checklist on this device, not verified remediation.

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