PyPI · virtualenv
virtualenv bash activate runs commands from an environment name with a backslash before $
The bash activate script escapes the environment name for only one of the two passes bash makes over PS1, so a
backslash in the name undoes the escaping and a name containing \$(...) runs as commands in the user's shell each
time bash draws the prompt.
src/virtualenv/activation/bash/activate.sh, the block that prepends the environment name to PS1.
The environment name: the environment directory's name, or the --prompt or VIRTUALENV_PROMPT value. An attacker
needs to influence it, for example through 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.
bash handles PS1 in two passes each time it draws the prompt: it first decodes backslash prompt escapes, turning \\
into \ and \$ into $ (or # for root), and then runs parameter expansion, command substitution and arithmetic
expansion on the result. Since 21.13.0 the script escapes backslashes, dollar signs and backticks in the name, but only
for the second pass, so the decode pass strips the escaping that a backslash in the name precedes. Releases before
21.13.0 do not escape the name at all. A bash running as root decodes \$ to #, so the payload shows the wrong text
there but runs nothing. zsh does no decode pass and is not affected.
$ virtualenv --prompt 'a\$(touch PWNED)' env
$ bash --norc --noprofile -c 'source env/bin/activate; printf "%s" "${PS1@P}"'
$ ls PWNED
PWNED
Arbitrary command execution in the shell of a user who sources the activate script of an environment whose name an
attacker influenced, with that user's privileges, once per prompt draw.
21.14.6 with bash 5.2.15 on Debian bookworm, as an unprivileged user and as root.
Set VIRTUAL_ENV_DISABLE_PROMPT=1 before you source activate, which leaves PS1 alone, or run shopt -u promptvars
if your prompt does not need expansion. Check the name of an environment you did not create before you source its
activate.
21.14.6
Fixed in 21.14.7. Under bash, activate now escapes backslashes, dollar signs and backticks for both passes, so the
example above runs nothing and the prompt shows the name as given. zsh keeps the single escaping it needs.
Fix: https://github.com/pypa/virtualenv/commit/c3104e02474b652832a9bbaae79f6e1696296932
Found while running the virtualenv test suite as root inside the Anthropic OSS Scanner build image.
Is your project exposed to this? Stateward checks every dependency on every pull request and flags it only if your code actually reaches it.
Check my repoSources: CISA KEV (public domain), OSV.dev & GitHub Advisory Database (CC-BY-4.0), FIRST EPSS, NVD/CWE (public domain). Served live from the Stateward advisory database.