libxml2: Fix CVE-2026-86137

This patch applies the upstream fix as referenced in [2],
using the commit shown in [1].

[1] https://github.com/GNOME/libxml2/commit/76fe08d97de88bfaef2f7d5cd27f11954cc5bee2
[2] https://nvd.nist.gov/vuln/detail/CVE-2026-86137

(From OE-Core rev: f91dd4ffea498d407893031da23cde93a58fb6f5)

Signed-off-by: Hetvi Thakar <hthakar@cisco.com>
Signed-off-by: Yoann Congal <yoann.congal@smile.fr>
Signed-off-by: Paul Barker <paul@pbarker.dev>

meta/recipes-core/libxml/libxml2/CVE-2026-86137.patch

@@ -0,0 +1,63 @@
+From a9d489b86e46188d1c0fde7dbd0aa8281596e6d6 Mon Sep 17 00:00:00 2001
+From: Hieu Le Minh <leminhhieu.opensource@gmail.com>
+Date: Sat, 18 Apr 2026 21:18:24 +0700
+Subject: [PATCH] xmlregexp: Prevent out-of-bounds read in NXT macro
+
+Fixes: https://gitlab.gnome.org/GNOME/libxml2/-/issues/1099
+
+CVE: CVE-2026-86137
+Upstream-Status: Backport [https://github.com/GNOME/libxml2/commit/76fe08d97de88bfaef2f7d5cd27f11954cc5bee2]
+
+Backport Changes:
+- Add the parser-context length field and allocation-failure guard required by
+  the Scarthgap 2.12.10 source, which lacks both pieces of the upstream
+  context.
+- The allocation-failure guard is completed by the subsequent
+  CVE-2026-86141.patch, which moves strlen() after the xmlStrdup() null check;
+  keep that patch after this one in SRC_URI.
+
+(cherry picked from commit 76fe08d97de88bfaef2f7d5cd27f11954cc5bee2)
+Signed-off-by: Hetvi Thakar <hthakar@cisco.com>
+---
+ xmlregexp.c | 13 +++++++++++--
+ 1 file changed, 11 insertions(+), 2 deletions(-)
+
+diff --git a/xmlregexp.c b/xmlregexp.c
+index f434a0cf..320a35ce 100644
+--- a/xmlregexp.c
++++ b/xmlregexp.c
+@@ -56,7 +56,9 @@
+     xmlRegexpErrCompile(ctxt, str);
+ #define NEXT ctxt->cur++
+ #define CUR (*(ctxt->cur))
+-#define NXT(index) (ctxt->cur[index])
++#define NXT(index)									\
++    (((size_t)(ctxt->cur + index - ctxt->string) < ctxt->len)				\
++      ? ctxt->cur[index] : 0)
+ 
+ #define NEXTL(l) ctxt->cur += l;
+ #define XML_REG_STRING_SEPARATOR '|'
+@@ -245,6 +247,7 @@ typedef xmlRegParserCtxt *xmlRegParserCtxtPtr;
+ struct _xmlAutomata {
+     xmlChar *string;
+     xmlChar *cur;
++    size_t len;
+ 
+     int error;
+     int neg;
+@@ -698,8 +701,14 @@ xmlRegNewParserCtxt(const xmlChar *string) {
+     if (ret == NULL)
+ 	return(NULL);
+     memset(ret, 0, sizeof(xmlRegParserCtxt));
+-    if (string != NULL)
++    if (string != NULL) {
+ 	ret->string = xmlStrdup(string);
++	ret->len = strlen((const char *) ret->string);
++        if (ret->string == NULL) {
++            xmlFree(ret);
++            return(NULL);
++        }
++    }
+     ret->cur = ret->string;
+     ret->neg = 0;
+     ret->negs = 0;

meta/recipes-core/libxml/libxml2_2.12.10.bb

@@ -32,6 +32,7 @@ SRC_URI += "http://www.w3.org/XML/Test/xmlts20130923.tar;subdir=${BP};name=testt
            file://CVE-2026-0992-03.patch \
            file://CVE-2026-1757.patch \
            file://CVE-2026-11979.patch \
+           file://CVE-2026-86137.patch \
            "
 
 SRC_URI[archive.sha256sum] = "c3d8c0c34aa39098f66576fe51969db12a5100b956233dc56506f7a8679be995"