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[PR #13212] Fix SetConsoleWindowInfo being able to crash ConPTY #29425

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opened 2026-01-31 09:34:50 +00:00 by claunia · 0 comments
claunia commented 2026-01-31 09:34:50 +00:00
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Original Pull Request: https://github.com/microsoft/terminal/pull/13212

State: closed
Merged: Yes

MSFT-33471786 is one of the most common crashes we have right now.
Memory dumps suggest that VtEngine::UpdateViewport is called with a rectangle
like (0, 46, 119, 29) (left, top, right, bottom), which is a rectangle of
negative height. When the _invalidMap is resized the negative size gets
turned into a very large unsigned integer, which results in an OOM exception,
crashing OpenConsole.

VtEngine::UpdateViewport is called by Renderer::_CheckViewportAndScroll
which holds a (cached) old and a new viewport. The old viewport was
(0, 46, 119, 75) which is exceedingly similar to the invalid, new viewport.
It's bottom coordinate is also coincidentally larger by exactly 46 (top).

The viewport comes from the SCREEN_INFORMATION class whose SetViewport
function was highly suspicious as it has a branch which updates the bottom
to be the buffer height, but leaves the top unmodified.

SCREEN_INFORMATION::SetViewport is called by SetConsoleWindowInfo which
processes user-provided data. A repro of the crash can be constructed with:

SMALL_RECT rect{0, 46, 119, 75};
SetConsoleWindowInfo(GetStdHandle(STD_OUTPUT_HANDLE), TRUE, &rect);

Closes #13193
Closes MSFT-33471786

Validation Steps Performed

Ensured the following code doesn't crash when run under Windows Terminal:

SMALL_RECT rect{0, 46, 119, 75};
SetConsoleWindowInfo(GetStdHandle(STD_OUTPUT_HANDLE), TRUE, &rect);
**Original Pull Request:** https://github.com/microsoft/terminal/pull/13212 **State:** closed **Merged:** Yes --- MSFT-33471786 is one of the most common crashes we have right now. Memory dumps suggest that `VtEngine::UpdateViewport` is called with a rectangle like `(0, 46, 119, 29)` (left, top, right, bottom), which is a rectangle of negative height. When the `_invalidMap` is resized the negative size gets turned into a very large unsigned integer, which results in an OOM exception, crashing OpenConsole. `VtEngine::UpdateViewport` is called by `Renderer::_CheckViewportAndScroll` which holds a (cached) old and a new viewport. The old viewport was `(0, 46, 119, 75)` which is exceedingly similar to the invalid, new viewport. It's bottom coordinate is also coincidentally larger by exactly 46 (top). The viewport comes from the `SCREEN_INFORMATION` class whose `SetViewport` function was highly suspicious as it has a branch which updates the bottom to be the buffer height, but leaves the top unmodified. `SCREEN_INFORMATION::SetViewport` is called by `SetConsoleWindowInfo` which processes user-provided data. A repro of the crash can be constructed with: ``` SMALL_RECT rect{0, 46, 119, 75}; SetConsoleWindowInfo(GetStdHandle(STD_OUTPUT_HANDLE), TRUE, &rect); ``` Closes #13193 Closes MSFT-33471786 ## Validation Steps Performed Ensured the following code doesn't crash when run under Windows Terminal: ``` SMALL_RECT rect{0, 46, 119, 75}; SetConsoleWindowInfo(GetStdHandle(STD_OUTPUT_HANDLE), TRUE, &rect); ```
claunia added the pull-request label 2026-01-31 09:34:50 +00:00
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Reference: starred/terminal#29425
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