Skip to content

C++: exclude printf implementation internals from uncontrolled format string sinks #21493

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Open
MarkLee131 wants to merge 4 commits into
base: main
Choose a base branch
from
+19 −1
Open

C++: exclude printf implementation internals from uncontrolled format string sinks #21493

Changes from all commits
Commits
Show all changes
4 commits
Select commit Hold shift + click to select a range
ff48ac5
C++: exclude printf implementation internals from format string sinks
MarkLee131 Mar 17, 2026
2c76e6e
use American spellings in documentation
MarkLee131 Mar 19, 2026
c155394
the [] syntax directly
MarkLee131 Mar 19, 2026
1ddf81c
Merge branch 'main' into fix/format-string-fp-in-printf-impl
MarkLee131 Mar 19, 2026
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
20 changes: 19 additions & 1 deletion cpp/ql/src/Security/CWE/CWE-134/UncontrolledFormatString.ql
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -23,13 +23,31 @@ import Flow::PathGraph

predicate isSource(FlowSource source, string sourceType) { sourceType = source.getSourceType() }

/**
* Holds if `f` is a printf-like function or a (possibly nested) wrapper
* that forwards a format-string parameter to one.
*
* Functions that *implement* printf-like behavior (e.g. a custom
* `vsnprintf` variant) internally parse the caller-supplied format string
* and build small, bounded, local format strings such as `"%d"` or `"%ld"`
* for inner `sprintf` calls. Taint that reaches those inner calls via the
* parsed format specifier is not exploitable, so sinks inside such
* functions should be excluded.
*/
Comment on lines +26 to +36
private predicate isPrintfImplementation(Function f) {
f instanceof PrintfLikeFunction
or
exists(PrintfLikeFunction printf | printf.wrapperFunction(f, _, _))
}

module Config implements DataFlow::ConfigSig {
predicate isSource(DataFlow::Node node) { isSource(node, _) }

predicate isSink(DataFlow::Node node) {
exists(PrintfLikeFunction printf |
printf.outermostWrapperFunctionCall([node.asExpr(), node.asIndirectExpr()], _)
)
) and
not isPrintfImplementation([node.asExpr(), node.asIndirectExpr()].getEnclosingFunction())
}

private predicate isArithmeticNonCharType(ArithmeticType type) {
Expand Down
Loading