Undefined behaviour in mprintf #5722
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Verify that specified parameters are in range. If parameters are too large, fail early on and avoid out of boundary accesses. Also do not read behind boundaries of illegal format strings. These are defensive measures since it is expected that format strings are well-formed. Format strings should not be modifiable by user input due to possible generic format string attacks.
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Thanks, but this seems to make test 557 fail sometimes. example |
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BTW, it would be awesome if we could also add test cases that reproduce these problems and then these fixes. Can you see if you can add that to lib557.c ? |
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I have added a test case for this. |
Stack overflows can occur with precisions for integers and floats.
Proof of concepts:
- curl_mprintf("%d, %.*1$d", 500, 1);
- curl_mprintf("%d, %+0500.*1$f", 500, 1);
Ideally, compile with -fsanitize=address which makes this undefined
behavior a bit more defined for debug purposes.
The format strings are valid. The overflows occur due to invalid
arguments. If these arguments are variables with contents controlled
by an attacker, the function's stack can be corrupted.
Also see CVE-2016-9586 which partially fixed the float aspect.
Signed-off-by: Tobias Stoeckmann <tobias@stoeckmann.org>
bagder
approved these changes
Jul 26, 2020
jay
pushed a commit
that referenced
this pull request
Jul 27, 2020
Stack overflows can occur with precisions for integers and floats.
Proof of concepts:
- curl_mprintf("%d, %.*1$d", 500, 1);
- curl_mprintf("%d, %+0500.*1$f", 500, 1);
Ideally, compile with -fsanitize=address which makes this undefined
behavior a bit more defined for debug purposes.
The format strings are valid. The overflows occur due to invalid
arguments. If these arguments are variables with contents controlled
by an attacker, the function's stack can be corrupted.
Also see CVE-2016-9586 which partially fixed the float aspect.
Signed-off-by: Tobias Stoeckmann <tobias@stoeckmann.org>
Closes #5722
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Thanks |
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Refactoring of mprintf code to prevent undefined behaviour (signed integer overflows and out of boundary accesses).