T09 · Insecure Skill Coding Practices
- Location
scripts/docker_analyzer.sh:113- Finding
Arbitrary Python Code Execution Through Unsafely Interpolated Image Name
- Content
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Vulnerability Details
File Location:
scripts/docker_analyzer.sh, lines 113–116
Vulnerability Type: Python code injection through an unquoted shell heredoc
Risk Level: HighVulnerable Code
bash python3 << PYEOF import subprocess, json image = "$image" try:Technical Analysis
The
optimizecommand reads an image name from its first command-line argument and stores it in the shell variableimage. It then uses an unquoted heredoc delimiter (PYEOF) to construct a Python program.Because the delimiter is unquoted, Bash performs parameter expansion within the heredoc before passing its contents to Python. The attacker-controlled value of
$imageis therefore inserted directly into Python source code inside a double-quoted string.An image argument containing a double quote can terminate that string and append arbitrary Python statements. A payload with the following structure demonstrates the injection primitive:
text "; __import__("os").system("malicious-command"); #After shell expansion, Python interprets the injected expression as executable source code. Execution occurs before the subsequent Docker operation can validate whether the supplied value is a legitimate image reference. The use of a list-form argument in the later
subprocess.check_outputcall does not mitigate this earlier source-code injection.Attack Path
- An attacker gains the ability to control or influence the image argument supplied to
docker-analyzer optimize. - The script assigns that argument to the
imageshell variable. - Bash expands
$imagewhile processing the unquoted heredoc. - A crafted quote terminates the intended Python string and introduces attacker-selected Python statements.
- The Python interpreter parses and executes those statements with the privileges of the Docker Analyzer process.
- The injected code can invoke operating-system commands, read accessible fi ...[truncated 915 chars]
- An attacker gains the ability to control or influence the image argument supplied to
- Remediation
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Remediation Suggestions
Do not interpolate shell-controlled data into generated Python source. Pass the image name as a positional argument and quote the heredoc delimiter so that Bash performs no expansion:
bash python3 - "$image" <<'PYEOF' import json import subprocess import sys image = sys.argv[1] try: out = subprocess.check_output( [ "docker", "history", "--no-trunc", "--format", "{{json .}}", image, ], stderr=subprocess.STDOUT, ).decode() # Continue processing the result. except Exception as exc: print("Error: {}".format(exc)) PYEOFAdditional hardening measures:
- Preserve list-form subprocess invocation and never use
shell=Truefor the image value. - Optionally validate image references against the syntax accepted by Docker as defense in depth, but do not treat validation as a substitute for separating data from code.
- Add regression tests using image values containing quotes, backslashes, command substitutions, newlines, semicolons, and Python comment characters.
- Run the analyzer with the least-privileged account possible and avoid unnecessary root or Docker daemon access.
- Review future heredocs and embedded-language blocks to ensure all delimiters are quoted whenever shell expansion is unnecessary.
- Preserve list-form subprocess invocation and never use