From ae9db77325abc0b4169b6bd0ac102c0e263cf3b7 Mon Sep 17 00:00:00 2001
From: lazerg <lazerg2@gmail.com>
Date: Fri, 7 Aug 2026 23:01:47 +0500
Subject: [PATCH] Fix GH-23106: mb_strpos() reads past the end of a truncated
 UTF-8 haystack

---
 NEWS                            |  2 ++
 ext/mbstring/mbstring.c         |  3 +++
 ext/mbstring/tests/gh23106.phpt | 22 ++++++++++++++++++++++
 3 files changed, 27 insertions(+)
 create mode 100644 ext/mbstring/tests/gh23106.phpt

diff --git a/NEWS b/NEWS
index ba832ef05888..84ef871ff953 100644
--- a/NEWS
+++ b/NEWS
@@ -17,6 +17,8 @@ PHP                                                                        NEWS
     offset in a non-UTF-8 encoding). (Eyüp Can Akman)
   . Fixed bug GH-21036 (mb_ereg_search_getregs() crashes after mb_eregi()
     invalidates the regex cache). (Matthias Goergens)
+  . Fixed bug GH-23106 (mb_strpos() reads past the end of a haystack ending in
+    a truncated UTF-8 sequence). (Lazizbek Ergashev)
 
 - Opcache:
   . Fixed bug GH-22857 (Function JIT emits wrong code for FETCH_OBJ_FUNC_ARG on a
diff --git a/ext/mbstring/mbstring.c b/ext/mbstring/mbstring.c
index 4893390a8264..6fbeb43fc1b4 100644
--- a/ext/mbstring/mbstring.c
+++ b/ext/mbstring/mbstring.c
@@ -1891,6 +1891,9 @@ static unsigned char* offset_to_pointer_utf8(unsigned char *str, unsigned char *
 			}
 			pos += u8_tbl[*pos];
 		}
+		if (pos > end) {
+			pos = end;
+		}
 		return pos;
 	}
 }
diff --git a/ext/mbstring/tests/gh23106.phpt b/ext/mbstring/tests/gh23106.phpt
new file mode 100644
index 000000000000..f55df0f2f081
--- /dev/null
+++ b/ext/mbstring/tests/gh23106.phpt
@@ -0,0 +1,22 @@
+--TEST--
+GH-23106 (mb_strpos() reads past the end of a haystack ending in a truncated UTF-8 sequence)
+--EXTENSIONS--
+mbstring
+--FILE--
+<?php
+var_dump(mb_strpos("AA\xf0\x90", "xyz", 3));
+var_dump(mb_strpos("AA\xf0\x90", "x", 3));
+var_dump(mb_strrpos("AA\xf0\x90", "A", 3));
+var_dump(mb_strrpos("AA\xf0\x90", "A", -1));
+try {
+    mb_strpos("AA\xf0\x90", "xyz", 4);
+} catch (ValueError $e) {
+    echo $e->getMessage(), "\n";
+}
+?>
+--EXPECT--
+bool(false)
+bool(false)
+bool(false)
+int(1)
+mb_strpos(): Argument #3 ($offset) must be contained in argument #1 ($haystack)