semgrep 0.9.0

Fast and syntax-aware semantic code pattern search for many languages: like grep but for code

Semgrep

semgrep is a tool for easily detecting and preventing bugs and anti-patterns in your codebase. It combines the convenience of grep with the correctness of syntactical and semantic search. Developers, DevOps engineers, and security engineers use semgrep to write code with confidence.

Try it now: https://semgrep.live

Overview

Language support:

Python	Javascript	Go	Java	C	Typescript	PHP
✅	✅	✅	✅	✅	Coming...	Coming...

Example patterns:

Pattern	Matches
$X == $X	if (node.id == node.id): ...
requests.get(..., verify=False, ...)	requests.get(url, timeout=3, verify=False)
os.system(...)	from os import system; system('echo semgrep')
$ELEMENT.innerHTML	el.innerHTML = "<img src='x' onerror='alert(`XSS`)'>";
$TOKEN.SignedString([]byte("..."))	ss, err := token.SignedString([]byte("HARDCODED KEY"))

→ see more example patterns in the live registry viewer

Installation

On macOS, binaries are available via Homebrew:

brew install returntocorp/semgrep/semgrep

On Ubuntu, an install script is available on each release here

./semgrep-v0.9.0-ubuntu-generic.sh

To try semgrep without installation, you can also run it via Docker:

docker run --rm -v "${PWD}:/home/repo" returntocorp/semgrep --help

Usage

Example Usage

Here is a simple Python example, test.py. We want to retrieve an object by ID:

def get_node(node_id, nodes):
    for node in nodes:
        if node.id == node.id:  # Oops, supposed to be 'node_id'
            return node
    return None

This is a bug. Let's use semgrep to find bugs like it, using a simple search pattern: $X == $X. It will find all places in our code where the left- and right-hand sides of a comparison are the same expression:

$ semgrep --lang python --pattern '$X == $X' test.py
test.py
3:        if node.id == node.id:  # Oops, supposed to be 'node_id'

Configuration

For simple patterns use the --lang and --pattern flags. This mode of operation is useful for quickly iterating on a pattern on a single file or folder:

semgrep --lang javascript --pattern 'eval(...)' path/to/file.js

Configuration Files

For advanced configuration use the --config flag. This flag automagically handles a multitude of input configuration types:

• --config <file|folder|yaml_url|tarball_url|registy_name>

In the absence of this flag, a default configuration is loaded from .semgrep.yml or multiple files matching .semgrep/**/*.yml.

Registry

As mentioned above, you may also specify a registry_name as configuration. r2c provides a registry of rules. These rules have been tuned on thousands of repositories using our analysis platform.

You can browse the registry at semgrep.live/r. To run a set of rules, use a rule ID or namespace.

# Run a specific rule
semgrep --config=https://semgrep.live/c/r/java.spring.security.audit.cookie-missing-samesite

# Run a set of rules
semgrep --config=https://semgrep.live/c/r/java.spring.security

The registry features rules for many programming errors, including security issues and correctness bugs. Security rules are annotated with CWE and OWASP metadata when applicable. OWASP rule coverage per language is displayed below.

Pattern Features

semgrep patterns make use of two primary features:

• Metavariables like $X, $WIDGET, or $USERS_2. Metavariable names can only contain uppercase characters, or _, or digits, and must start with an uppercase character or _. Names like $x or $some_value are invalid. Metavariables are used to track a variable across a specific code scope.
• The ... (ellipsis) operator. The ellipsis operator abstracts away sequences of zero or more arguments, statements, characters, and more.

For example,

$FILE = open(...)

will find all occurrences in your code where the result of an open() call with zero or more arguments is assigned to a variable.

Composing Patterns

You can also construct rules by composing multiple patterns together.

Let's consider an example:

rules:
  - id: open-never-closed
    patterns:
      - pattern: $FILE = open(...)
      - pattern-not-inside: |
          $FILE = open(...)
          ...
          $FILE.close()
    message: "file object opened without corresponding close"
    languages: [python]
    severity: ERROR

This rule looks for files that are opened but never closed. It accomplishes this by looking for the open(...) pattern and not a following close() pattern. The $FILE metavariable ensures that the same variable name is used in the open and close calls. The ellipsis operator allows for any arguments to be passed to open and any sequence of code statements in-between the open and close calls. We don't care how open is called or what happens up to a close call, we just need to make sure close is called.

For more information on rule fields like patterns and pattern-not-inside see the configuration documentation.

Equivalences

Equivalences are another key concept in semgrep. semgrep automatically searches for code that is semantically equivalent. For example, the following patterns are semantically equivalent. The pattern subprocess.Popen(...) will fire on both.

subprocess.Popen("ls")

from subprocess import Popen as sub_popen

result = sub_popen("ls")

For a full list of semgrep feature support by language see the language matrix.

Programmatic Usage

To integrate semgrep's results with other tools, you can get results in machine-readable JSON format with the --json option, or formatted according to the SARIF standard with the --sarif flag.

See our output documentation for details.

Resources

• Semgrep presentation and slides at Bay Area OWASP meetup. Check out the r2c YouTube channel for more videos.
• Pattern features documentation
• Configuration files documentation
• Integrations
• Output
• Development
• Bug reports

Contribution

semgrep is LGPL-licensed, feel free to help out: CONTRIBUTING.

semgrep is a frontend to a larger program analysis library named pfff. pfff began and was open-sourced at Facebook but is now archived. The primary maintainer now works at r2c. semgrep was originally named sgrep and was renamed to avoid collisons with existing projects.

Commercial Support

semgrep is proudly supported by r2c. We're hiring!

Interested in a fully-supported, hosted version of semgrep? Drop your email and we'll ping you!