From fdf8ef0f0810e3d365cdd5160de43db46f57ed03 Mon Sep 17 00:00:00 2001
From: tlsbollei <170938166+tlsbollei@users.noreply.github.com>
Date: Wed, 8 Apr 2026 21:43:46 +0200
Subject: [PATCH] Add runtime type checks to f_string_indexes

This fixes CVE-2026-39956.
---
 src/builtin.c | 8 ++++++++
 tests/jq.test | 9 +++++++++
 2 files changed, 17 insertions(+)

diff --git a/src/builtin.c b/src/builtin.c
index 90a3af2d..d33e9fb1 100644
--- a/src/builtin.c
+++ b/src/builtin.c
@@ -1306,6 +1306,14 @@ static jv f_string_explode(jq_state *jq, jv a) {
 }
 
 static jv f_string_indexes(jq_state *jq, jv a, jv b) {
+  if (jv_get_kind(a) != JV_KIND_STRING) {
+    jv_free(b);
+    return type_error(a, "cannot be searched, as it is not a string");
+  }
+  if (jv_get_kind(b) != JV_KIND_STRING) {
+    jv_free(a);
+    return type_error(b, "is not a string");
+  }
   return jv_string_indexes(a, b);
 }
 
diff --git a/tests/jq.test b/tests/jq.test
index 169a7ac8..4a84e96c 100644
--- a/tests/jq.test
+++ b/tests/jq.test
@@ -1549,6 +1549,15 @@ split("")
 "xababababax"
 [1,7,[1,3,5,7]]
 
+# _strindices is used by indices/1 but is callable
+try _strindices("abc") catch .
+123
+"number (123) cannot be searched, as it is not a string"
+
+try _strindices(123) catch .
+"abc"
+"number (123) is not a string"
+
 # trim
 # \u000b is vertical tab (\v not supported by json)
 map(trim), map(ltrim), map(rtrim)