From: Stan Ulbrych <stan@python.org>
Date: Mon, 13 Apr 2026 01:14:54 +0000 (+0100)
Subject: gh-148395: Fix a possible UAF in `{LZMA,BZ2,_Zlib}Decompressor` (GH-148396)
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=8fc66aef6d7b3ae58f43f5c66f9366cc8cbbfcd2;p=thirdparty%2FPython%2Fcpython.git

gh-148395: Fix a possible UAF in `{LZMA,BZ2,_Zlib}Decompressor` (GH-148396)

Fix dangling input pointer after `MemoryError` in _lzma/_bz2/_ZlibDecompressor.decompress
---

diff --git a/Misc/NEWS.d/next/Security/2026-04-10-16-28-21.gh-issue-148395.kfzm0G.rst b/Misc/NEWS.d/next/Security/2026-04-10-16-28-21.gh-issue-148395.kfzm0G.rst
new file mode 100644
index 000000000000..9502189ab199
--- /dev/null
+++ b/Misc/NEWS.d/next/Security/2026-04-10-16-28-21.gh-issue-148395.kfzm0G.rst
@@ -0,0 +1,5 @@
+Fix a dangling input pointer in :class:`lzma.LZMADecompressor`,
+:class:`bz2.BZ2Decompressor`, and internal :class:`!zlib._ZlibDecompressor`
+when memory allocation fails with :exc:`MemoryError`, which could let a
+subsequent :meth:`!decompress` call read or write through a stale pointer to
+the already-released caller buffer.
diff --git a/Modules/_bz2module.c b/Modules/_bz2module.c
index d6c5c39ff910..4bff90e6fd2b 100644
--- a/Modules/_bz2module.c
+++ b/Modules/_bz2module.c
@@ -571,6 +571,7 @@ decompress(BZ2Decompressor *d, char *data, size_t len, Py_ssize_t max_length)
     return result;
 
 error:
+    bzs->next_in = NULL;
     Py_XDECREF(result);
     return NULL;
 }
diff --git a/Modules/_lzmamodule.c b/Modules/_lzmamodule.c
index 3c391675d7b9..00ee68dcea2d 100644
--- a/Modules/_lzmamodule.c
+++ b/Modules/_lzmamodule.c
@@ -1100,6 +1100,7 @@ decompress(Decompressor *d, uint8_t *data, size_t len, Py_ssize_t max_length)
     return result;
 
 error:
+    lzs->next_in = NULL;
     Py_XDECREF(result);
     return NULL;
 }
diff --git a/Modules/zlibmodule.c b/Modules/zlibmodule.c
index f67434ecdc90..9c5820fbe97a 100644
--- a/Modules/zlibmodule.c
+++ b/Modules/zlibmodule.c
@@ -1669,6 +1669,7 @@ decompress(ZlibDecompressor *self, uint8_t *data,
     return result;
 
 error:
+    self->zst.next_in = NULL;
     Py_XDECREF(result);
     return NULL;
 }