From: Amaury Couderc <[email protected]> CVE-2026-7210 is a hash-flooding denial-of-service vulnerability in Python's XML parsing modules (xml.parsers.expat, xml.etree.ElementTree). An attacker can craft XML input that forces O(n²) hash collisions in libexpat's internal name dictionary, causing excessive CPU consumption.
The previous mitigation seeded libexpat's hash function with only 4 bytes of entropy, which is insufficient against a determined attacker. This patch upgrades to XML_SetHashSalt16Bytes (libexpat >= 2.8.0), providing a full 16-byte secret. Older expat versions fall back gracefully to the legacy XML_SetHashSalt via a runtime NULL check. Backport patch to fix CVE-2026-7210. https://nvd.nist.gov/vuln/detail/CVE-2026-7210 Upstream fix: https://github.com/python/cpython/commit/24b8f12544468e4cedf5bfbe25442fcd495391e4 -- Changes from Upstream -- Replace compile-time version checks with runtime detection of the XML_SetHashSalt16Bytes function using #pragma weak. This allows using backported security fixes from expat even when version macros haven't been bumped (in thus case expat 2.6.4 with CVE-2026-41080). - Add weak symbol declaration for XML_SetHashSalt16Bytes - Convert newxmlparseobject() version check to runtime NULL check - Convert pyexpat_exec() CAPI export check to runtime NULL check Tested with ptest: Before: PASSED: 40019, FAILED: 0, SKIPPED: 1882 After: PASSED: 40020, FAILED: 0, SKIPPED: 1882 CVE: CVE-2026-7210 Signed-off-by: Amaury Couderc <[email protected]> --- Changes v3 -> v4: - Replace compile-time #if XML_COMBINED_VERSION >= 20800 guards with runtime detection using #pragma weak XML_SetHashSalt16Bytes. Our backported expat 2.6.4 (with CVE-2026-41080 patches) exports XML_SetHashSalt16Bytes but does not bump XML_COMBINED_VERSION to 20800, so the v3 version-based check left the 16-byte path as dead code. The weak symbol approach resolves the function at link time when available, activating full 16-byte entropy protection. - Add [yocto: ...] note in the inner patch header documenting the deviation from upstream. --- .../python/python3/CVE-2026-7210.patch | 148 ++++++++++++++++++ .../python/python3_3.12.13.bb | 1 + 2 files changed, 149 insertions(+) create mode 100644 meta/recipes-devtools/python/python3/CVE-2026-7210.patch diff --git a/meta/recipes-devtools/python/python3/CVE-2026-7210.patch b/meta/recipes-devtools/python/python3/CVE-2026-7210.patch new file mode 100644 index 0000000000..029eb713e4 --- /dev/null +++ b/meta/recipes-devtools/python/python3/CVE-2026-7210.patch @@ -0,0 +1,148 @@ +From 2ed6138dea0bc94c726f879501e4525712e885d1 Mon Sep 17 00:00:00 2001 +From: Stan Ulbrych <[email protected]> +Date: Sun, 10 May 2026 18:36:26 +0100 +Subject: [PATCH] gh-149018: Use `XML_SetHashSalt16Bytes` in + `pyexpat`/`_elementtree` when possible (#149023) + + +CVE: CVE-2026-7210 +Upstream-Status: Backport [https://github.com/python/cpython/commit/24b8f12544468e4cedf5bfbe25442fcd495391e4] + +[yocto: Use weak symbol detection for XML_SetHashSalt16Bytes instead of +XML_COMBINED_VERSION >= 20800, since our backported expat 2.6.4 provides +the function but does not bump the version macros.] + +Signed-off-by: Amaury Couderc <[email protected]> +--- + Include/pyexpat.h | 3 +++ + Include/pyhash.h | 8 +++++--- + .../2026-04-26-19-30-45.gh-issue-149018.a9SqWb.rst | 3 +++ + Modules/_elementtree.c | 8 ++++++-- + Modules/pyexpat.c | 22 ++++++++++++++++------ + 5 files changed, 33 insertions(+), 11 deletions(-) + create mode 100644 Misc/NEWS.d/next/Security/2026-04-26-19-30-45.gh-issue-149018.a9SqWb.rst + +diff --git a/Include/pyexpat.h b/Include/pyexpat.h +index 04548b7684a..d28d6828975 100644 +--- a/Include/pyexpat.h ++++ b/Include/pyexpat.h +@@ -57,6 +57,9 @@ struct PyExpat_CAPI + XML_Parser parser, unsigned long long activationThresholdBytes); + XML_Bool (*SetAllocTrackerMaximumAmplification)( + XML_Parser parser, float maxAmplificationFactor); ++ /* might be NULL for expat < 2.8.0 */ ++ XML_Bool (*SetHashSalt16Bytes)( ++ XML_Parser parser, const uint8_t entropy[16]); + /* always add new stuff to the end! */ + }; + +diff --git a/Include/pyhash.h b/Include/pyhash.h +index 182d223fab1..ec359bd2f35 100644 +--- a/Include/pyhash.h ++++ b/Include/pyhash.h +@@ -39,14 +39,14 @@ PyAPI_FUNC(Py_hash_t) _Py_HashBytes(const void*, Py_ssize_t); + * pppppppp ssssssss ........ fnv -- two Py_hash_t + * k0k0k0k0 k1k1k1k1 ........ siphash -- two uint64_t + * ........ ........ ssssssss djbx33a -- 16 bytes padding + one Py_hash_t +- * ........ ........ eeeeeeee pyexpat XML hash salt ++ * eeeeeeee eeeeeeee eeeeeeee pyexpat XML hash salt + * + * memory layout on 32 bit systems + * cccccccc cccccccc cccccccc uc + * ppppssss ........ ........ fnv -- two Py_hash_t + * k0k0k0k0 k1k1k1k1 ........ siphash -- two uint64_t (*) + * ........ ........ ssss.... djbx33a -- 16 bytes padding + one Py_hash_t +- * ........ ........ eeee.... pyexpat XML hash salt ++ * eeeeeeee eeeeeeee eeee.... pyexpat XML hash salt + * + * (*) The siphash member may not be available on 32 bit platforms without + * an unsigned int64 data type. +@@ -71,7 +71,9 @@ typedef union { + Py_hash_t suffix; + } djbx33a; + struct { +- unsigned char padding[16]; ++ /* 16 bytes for XML_SetHashSalt16Bytes */ ++ uint8_t hashsalt16[16]; ++ /* 4/8 bytes for legacy XML_SetHashSalt */ + Py_hash_t hashsalt; + } expat; + } _Py_HashSecret_t; +diff --git a/Misc/NEWS.d/next/Security/2026-04-26-19-30-45.gh-issue-149018.a9SqWb.rst b/Misc/NEWS.d/next/Security/2026-04-26-19-30-45.gh-issue-149018.a9SqWb.rst +new file mode 100644 +index 00000000000..d1b5b368684 +--- /dev/null ++++ b/Misc/NEWS.d/next/Security/2026-04-26-19-30-45.gh-issue-149018.a9SqWb.rst +@@ -0,0 +1,3 @@ ++Improved protection against XML hash-flooding attacks in ++:mod:`xml.parsers.expat` and :mod:`xml.etree.ElementTree` when Python is ++compiled with libExpat 2.8.0 or later. +diff --git a/Modules/_elementtree.c b/Modules/_elementtree.c +index 56d1508af13..941376613b0 100644 +--- a/Modules/_elementtree.c ++++ b/Modules/_elementtree.c +@@ -3657,8 +3657,12 @@ _elementtree_XMLParser___init___impl(XMLParserObject *self, PyObject *target, + PyErr_NoMemory(); + return -1; + } +- /* expat < 2.1.0 has no XML_SetHashSalt() */ +- if (EXPAT(st, SetHashSalt) != NULL) { ++ // Prefer 16-byte entropy, only expat >= 2.8.0. See gh-149018 ++ if (EXPAT(st, SetHashSalt16Bytes) != NULL) { ++ EXPAT(st, SetHashSalt16Bytes)(self->parser, ++ _Py_HashSecret.expat.hashsalt16); ++ } ++ else if (EXPAT(st, SetHashSalt) != NULL) { + EXPAT(st, SetHashSalt)(self->parser, + (unsigned long)_Py_HashSecret.expat.hashsalt); + } +diff --git a/Modules/pyexpat.c b/Modules/pyexpat.c +index 79492ca5c4f..47e3a1b2c00 100644 +--- a/Modules/pyexpat.c ++++ b/Modules/pyexpat.c +@@ -14,6 +14,11 @@ + + #include "pyexpat.h" + ++/* Use weak symbol to detect XML_SetHashSalt16Bytes at link time. ++ This allows using the backported function from expat even when the ++ version macros have not been bumped (e.g. expat 2.6.4 + CVE-2026-41080). */ ++#pragma weak XML_SetHashSalt16Bytes ++ + /* Do not emit Clinic output to a file as that wreaks havoc with conditionally + included methods. */ + /*[clinic input] +@@ -1388,10 +1393,16 @@ newxmlparseobject(pyexpat_state *state, const char *encoding, + Py_DECREF(self); + return NULL; + } +-#if XML_COMBINED_VERSION >= 20100 +- /* This feature was added upstream in libexpat 2.1.0. */ +- XML_SetHashSalt(self->itself, +- (unsigned long)_Py_HashSecret.expat.hashsalt); ++ /* Prefer 16-byte entropy (expat >= 2.8.0 or backported). */ ++ if (XML_SetHashSalt16Bytes != NULL) { ++ XML_SetHashSalt16Bytes(self->itself, _Py_HashSecret.expat.hashsalt16); ++ } ++#if XML_COMBINED_VERSION >= 20100 ++ else { ++ /* This feature was added upstream in libexpat 2.1.0. */ ++ XML_SetHashSalt(self->itself, ++ (unsigned long)_Py_HashSecret.expat.hashsalt); ++ } + #endif + XML_SetUserData(self->itself, (void *)self); + XML_SetUnknownEncodingHandler(self->itself, +@@ -2257,6 +2267,12 @@ pyexpat_exec(PyObject *mod) + #else + capi->SetHashSalt = NULL; + #endif ++ /* Detect at runtime via weak symbol */ ++ if (XML_SetHashSalt16Bytes != NULL) { ++ capi->SetHashSalt16Bytes = XML_SetHashSalt16Bytes; ++ } else { ++ capi->SetHashSalt16Bytes = NULL; ++ } + #if XML_COMBINED_VERSION >= 20600 + capi->SetReparseDeferralEnabled = XML_SetReparseDeferralEnabled; + #else diff --git a/meta/recipes-devtools/python/python3_3.12.13.bb b/meta/recipes-devtools/python/python3_3.12.13.bb index de174f7bfd..b6ceb0c634 100644 --- a/meta/recipes-devtools/python/python3_3.12.13.bb +++ b/meta/recipes-devtools/python/python3_3.12.13.bb @@ -47,6 +47,7 @@ SRC_URI = "http://www.python.org/ftp/python/${PV}/Python-${PV}.tar.xz \ file://CVE-2026-11940.patch \ file://CVE-2026-11972.patch \ file://CVE-2026-9669.patch \ + file://CVE-2026-7210.patch \ " SRC_URI:append:class-native = " \ -- 2.34.1
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