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Golang: Mark filepath.IsLocal as a tainted-path sanitizer guard #20056

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Merged
merged 3 commits into from
Jul 15, 2025
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Golang: Mark filepath.IsLocal as a tainted-path sanitizer guard #20056

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c8eefb7
Golang: Mark filepath.IsLocal as a tainted-path sanitizer guard
smowton Jul 15, 2025
ac72f85
Change note
smowton Jul 15, 2025
b71f9ae
Fix function qname
smowton Jul 15, 2025
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16 changes: 16 additions & 0 deletions go/ql/lib/semmle/go/security/TaintedPathCustomizations.qll
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Original file line number Diff line number Diff line change
Expand Up @@ -243,4 +243,20 @@ module TaintedPath {

override predicate checks(Expr e, boolean branch) { regexpFunctionChecksExpr(this, e, branch) }
}

/**
* A call of the form `filepath.IsLocal(path)` considered as a sanitizer guard for `path`.
*/
class IsLocalCheck extends SanitizerGuard, DataFlow::CallNode {
IsLocalCheck() {
exists(Function f |
f.hasQualifiedName("path/filepath", "IsLocal") and
this = f.getACall()
)
}

override predicate checks(Expr e, boolean branch) {
e = this.getArgument(0).asExpr() and branch = true
}
}
}
4 changes: 4 additions & 0 deletions go/ql/src/change-notes/2025-07-15-islocal-sanitizer.md
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@@ -0,0 +1,4 @@
---
category: minorAnalysis
---
* `filepath.IsLocal` is now recognised as a sanitizer against path-traversal and related vulnerabilities.
6 changes: 6 additions & 0 deletions go/ql/test/query-tests/Security/CWE-022/TaintedPath.go
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Expand Up @@ -93,4 +93,10 @@ func handler(w http.ResponseWriter, r *http.Request) {
}

data, _ = ioutil.ReadFile(part.FileName())

// GOOD: An attempt has been made to prevent path traversal
if filepath.IsLocal(tainted_path) {
data, _ = ioutil.ReadFile(tainted_path)
Comment on lines +98 to +99
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Copilot AI Jul 15, 2025

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The filepath.IsLocal() check alone may not provide complete path traversal protection. Consider combining it with additional validation such as filepath.Clean() or checking against an allowlist of permitted directories, as IsLocal() only validates that the path doesn't escape the current directory but doesn't prevent access to sensitive files within it.

Suggested change
if filepath.IsLocal(tainted_path) {
data, _ = ioutil.ReadFile(tainted_path)
cleanedPath := filepath.Clean(tainted_path)
allowedDir := "/allowed/directory" // Replace with the actual allowed directory
if filepath.IsLocal(cleanedPath) && strings.HasPrefix(cleanedPath, allowedDir) {
data, _ = ioutil.ReadFile(cleanedPath)

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w.Write(data)
}
}