Security Analysis in Psalm
Psalm can attempt to find connections between user-controlled input (like
$_GET['name']) and places that we don’t want unescaped user-controlled input to end up (like
echo "<h1>$name</h1>" by looking at the ways that data flows through your application (via assignments, function/method calls and array/property access).
You can enable this mode with the
--taint-analysis command line flag. When taint analysis is enabled, no other analysis is performed.
Tainted input is anything that can be controlled, wholly or in part, by a user of your application. In taint analysis, tainted input is called a taint source.
Taint analysis tracks how data flows from taint sources into taint sinks. Taint sinks are places you really don’t want untrusted data to end up.
<div id="section_<?= $id ?>">
$pdo->exec("select * from users where name='" . $name . "'")
Psalm recognises a number of taint types by default, defined in the Psalm\Type\TaintKind class:
text- used for strings that could be user-controlled
sql- used for strings that could contain SQL
html- used for strings that could contain angle brackets or unquoted strings
shell- used for strings that could contain shell commands
user_secret- used for strings that could contain user-supplied secrets
system_secret- used for strings that could contain system secrets
You're also free to define your own taint types when defining custom taint sources – they're just strings.
Psalm currently defines three default taint sources: the
$_COOKIE server variables.
You can also define your own taint sources.
Psalm currently defines a number of different for builtin functions and methods, including
You can also define your own taint sinks.
Nobody likes to wade through a ton of false-positives – here’s a guide to avoiding them.
Using Baseline With Taint Analysis
Since taint analysis is performed separately from other static code analysis, it makes sense to use a separate baseline for it.
You can use --use-baseline=PATH option to set a different baseline for taint analysis.