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gh-161060: Fix pyexpat crash when the default handler is cleared - #161061
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Expat calls the default handler once per 1024-byte piece of a token that needs encoding conversion. Install a no-op instead of NULL when the handler is cleared after an error or unset from within a callback, as is already done for the character data handler.
gpshead
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needs backport to 3.14
gpshead
marked this pull request as ready for review
November 1, 2026 06:00
The handler setter only installs the no-op handler in place of NULL while in_callback is set, but the trampolines reset it before releasing the handler's result. A destructor run at that point could still set the default handler to None, removing it while Expat was passing a long token to it in pieces. Also test unsetting DefaultHandlerExpand from within a callback, and reword the NEWS entry and a comment.
gpshead
enabled auto-merge (squash)
November 12, 2026 00:09
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Thanks @gpshead for the PR 🌮🎉.. I'm working now to backport this PR to: 3.14, 3.15. |
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Sorry, @gpshead, I could not cleanly backport this to Please backport manually with cherry_picker, see the devguide for more information. |
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GH-161842 is a backport of this pull request to the 3.15 branch. |
gpshead
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Nov 12, 2026
…ed (GH-161061) (#161842) gh-161060: Fix pyexpat crash when the default handler is cleared (GH-161061) Expat calls the default handler once per 1024-byte piece of a token that needs encoding conversion. Install a no-op instead of NULL when the handler is cleared after an error or unset from within a callback, as is already done for the character data handler. ANT-2026-0SJB3WWC (cherry picked from commit eb21dea) Co-authored-by: Gregory P. Smith <68491+gpshead@users.noreply.github.com>
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GH-161846 is a backport of this pull request to the 3.14 branch. |
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Expat calls the default handler once per 1024-byte piece of a token that needs encoding conversion and re-reads the handler pointer between pieces, so pyexpat must not set it to NULL from inside a callback. When handlers are cleared after an error, or
DefaultHandler/DefaultHandlerExpandis set toNonefrom inside a callback, install the existing no-op handler instead, as has been done for the character data handler since gh-42389. The Python-level handlers are still cleared, so no Python code runs after an error, and the handler setters are called in the same order, so the internal-entity expansion setting ends up as before.Fixes #161060
ANT-2026-0SJB3WWC
xml.parsers.expatcrashes whenDefaultHandlerraises on a long non-UTF-8 token #161060