diff --git a/meta/recipes-core/expat/expat/CVE-2026-77214.patch b/meta/recipes-core/expat/expat/CVE-2026-77214.patch
new file mode 100644
index 0000000000..6d74648705
--- /dev/null
+++ b/meta/recipes-core/expat/expat/CVE-2026-77214.patch
@@ -0,0 +1,106 @@
+From 4d9b1c499ecb66323260a7274edcf86c5eab0517 Mon Sep 17 00:00:00 2001
+From: Filippo Tedeschi <filippotedeschi98@gmail.com>
+Date: Fri, 25 Sep 2026 19:51:10 +0200
+Subject: [PATCH] lib|tests: Validate len against buffer capacity in
+ XML_ParseBuffer
+
+In XML_ParseBuffer(), if len exceeds the unoccupied capacity of the
+internal buffer (EXPAT_SAFE_PTR_DIFF(m_bufferLim, m_bufferEnd)),
+parser->m_bufferEnd was previously advanced past parser->m_bufferLim.
+This violated the parser's internal pointer invariant (m_bufferEnd <=
+m_bufferLim) and caused callProcessor() to read unallocated or
+uninitialized heap memory beyond the buffer bounds.
+
+Validate that len <= EXPAT_SAFE_PTR_DIFF(m_bufferLim, m_bufferEnd) for
+both XML_INITIALIZED and XML_PARSING states. If len exceeds the
+available buffer capacity, return XML_STATUS_ERROR with
+XML_ERROR_INVALID_ARGUMENT.
+
+Also add test_parse_buffer_exceeds_buffer in tests/basic_tests.c.
+
+Co-authored-by: Sebastian Pipping <sebastian@pipping.org>
+Signed-off-by: Filippo Tedeschi <filippotedeschi98@gmail.com>
+
+CVE: CVE-2026-77214
+Upstream-Status: Backport [https://github.com/libexpat/libexpat/commit/4d9b1c499ecb66323260a7274edcf86c5eab0517]
+Signed-off-by: Peter Marko <peter.marko@siemens.com>
+---
+ lib/xmlparse.c      |  5 +++++
+ tests/basic_tests.c | 41 +++++++++++++++++++++++++++++++++++++++++
+ 2 files changed, 46 insertions(+)
+
+diff --git a/lib/xmlparse.c b/lib/xmlparse.c
+index 08ef9f72..6e3af97b 100644
+--- a/lib/xmlparse.c
++++ b/lib/xmlparse.c
+@@ -2465,6 +2465,11 @@ XML_ParseBuffer(XML_Parser parser, int len, int isFinal) {
+     parser->m_parsingStatus.parsing = XML_PARSING;
+   }
+ 
++  if (len > EXPAT_SAFE_PTR_DIFF(parser->m_bufferLim, parser->m_bufferEnd)) {
++    parser->m_errorCode = XML_ERROR_INVALID_ARGUMENT;
++    return XML_STATUS_ERROR;
++  }
++
+   // Detect and avoid integer overflow
+   if ((uint64_t)len > UINT64_MAX - parser->m_parseEndByteIndex) {
+     parser->m_errorCode = XML_ERROR_NO_MEMORY;
+diff --git a/tests/basic_tests.c b/tests/basic_tests.c
+index 06268469..35e17d31 100644
+--- a/tests/basic_tests.c
++++ b/tests/basic_tests.c
+@@ -3605,6 +3605,46 @@ START_TEST(test_negative_len_parse_buffer) {
+ }
+ END_TEST
+ 
++/* Test XML_ParseBuffer rejects calls where len exceeds available buffer */
++START_TEST(test_parse_buffer_exceeds_buffer) {
++  for (int isFinal = 0; isFinal < 2; isFinal++) {
++    set_subtest("isFinal=%d", isFinal);
++
++    XML_Parser parser = XML_ParserCreate(NULL);
++
++    /* Calling XML_ParseBuffer without any prior XML_GetBuffer call */
++    if (XML_ParseBuffer(parser, 10, isFinal) != XML_STATUS_ERROR)
++      fail("XML_ParseBuffer without XML_GetBuffer was expected to fail.");
++    if (XML_GetErrorCode(parser) != XML_ERROR_NO_BUFFER)
++      fail("Expected XML_ERROR_NO_BUFFER.");
++
++    /* Acquire a small buffer */
++    void *const buffer = XML_GetBuffer(parser, 10);
++    if (buffer == NULL)
++      fail("XML_GetBuffer failed.");
++
++    /* Calling XML_ParseBuffer with len exceeding available buffer capacity */
++    if (XML_ParseBuffer(parser, 10000, isFinal) != XML_STATUS_ERROR)
++      fail("XML_ParseBuffer with len > capacity was expected to fail.");
++    if (XML_GetErrorCode(parser) != XML_ERROR_INVALID_ARGUMENT)
++      fail("Expected XML_ERROR_INVALID_ARGUMENT.");
++
++    /* Valid parse */
++    memcpy(buffer, "<r></r>", 7);
++    if (XML_ParseBuffer(parser, 7, XML_FALSE) != XML_STATUS_OK)
++      xml_failure(parser);
++
++    /* Subsequent XML_ParseBuffer where len exceeds remaining capacity */
++    if (XML_ParseBuffer(parser, 10000, isFinal) != XML_STATUS_ERROR)
++      fail("XML_ParseBuffer on subsequent chunk was expected to fail.");
++    if (XML_GetErrorCode(parser) != XML_ERROR_INVALID_ARGUMENT)
++      fail("Expected XML_ERROR_INVALID_ARGUMENT.");
++
++    XML_ParserFree(parser);
++  }
++}
++END_TEST
++
+ /* Test odd corners of the XML_GetBuffer interface */
+ static enum XML_Status
+ get_feature(enum XML_FeatureEnum feature_id, long *presult) {
+@@ -7054,6 +7094,7 @@ make_basic_test_case(Suite *s) {
+   tcase_add_test(tc_basic, test_empty_parse);
+   tcase_add_test(tc_basic, test_negative_len_parse);
+   tcase_add_test(tc_basic, test_negative_len_parse_buffer);
++  tcase_add_test(tc_basic, test_parse_buffer_exceeds_buffer);
+   tcase_add_test(tc_basic, test_get_buffer_1);
+   tcase_add_test(tc_basic, test_get_buffer_2);
+ #if XML_CONTEXT_BYTES > 0
diff --git a/meta/recipes-core/expat/expat_2.8.3.bb b/meta/recipes-core/expat/expat_2.8.3.bb
index 3a179db62c..02a8536440 100644
--- a/meta/recipes-core/expat/expat_2.8.3.bb
+++ b/meta/recipes-core/expat/expat_2.8.3.bb
@@ -19,6 +19,7 @@ SRC_URI = "${GITHUB_BASE_URI}/download/R_${VERSION_TAG}/expat-${PV}.tar.bz2  \
            file://CVE-2026-93990-01.patch \
            file://CVE-2026-93990-02.patch \
            file://CVE-2026-102633.patch \
+           file://CVE-2026-77214.patch \
            "
 
 GITHUB_BASE_URI = "https://github.com/libexpat/libexpat/releases/"