From 6fd190d8258661a7109cff7d4fd67a9cd6f36950 Mon Sep 17 00:00:00 2001
From: Krishnan Prashanth <kprashanth@nvidia.com>
Date: Wed, 15 Jul 2026 22:34:16 -0700
Subject: [PATCH] fix(frontend): reject nested chat_template in
 chat_template_args

Signed-off-by: Krishnan Prashanth <kprashanth@nvidia.com>
---
 .../src/protocols/openai/chat_completions.rs  |  1 +
 lib/llm/src/protocols/openai/validate.rs      | 30 +++++++++++++++++++
 2 files changed, 31 insertions(+)

diff --git a/lib/llm/src/protocols/openai/chat_completions.rs b/lib/llm/src/protocols/openai/chat_completions.rs
index 2144f5dbc8cf..4bae17c96997 100644
--- a/lib/llm/src/protocols/openai/chat_completions.rs
+++ b/lib/llm/src/protocols/openai/chat_completions.rs
@@ -531,6 +531,7 @@ impl OpenAIOutputOptionsProvider for NvCreateChatCompletionRequest {
 impl ValidateRequest for NvCreateChatCompletionRequest {
     fn validate(&self) -> Result<(), anyhow::Error> {
         validate::validate_no_unsupported_fields(&self.unsupported_fields)?;
+        validate::validate_chat_template_args(self.chat_template_args.as_ref())?;
         validate::validate_messages(&self.inner.messages)?;
         validate::validate_model(&self.inner.model)?;
         // none for store
diff --git a/lib/llm/src/protocols/openai/validate.rs b/lib/llm/src/protocols/openai/validate.rs
index 0c7f4b0bc2bd..c39712c27d1f 100644
--- a/lib/llm/src/protocols/openai/validate.rs
+++ b/lib/llm/src/protocols/openai/validate.rs
@@ -804,6 +804,19 @@ where
     Ok(Some(value))
 }
 
+/// A nested `chat_template` bypasses Dynamo's top-level rejection and is
+/// promoted into the rendered template, so block it for every chat processor.
+pub fn validate_chat_template_args(
+    chat_template_args: Option<&std::collections::HashMap<String, serde_json::Value>>,
+) -> Result<(), anyhow::Error> {
+    if let Some(args) = chat_template_args
+        && args.contains_key("chat_template")
+    {
+        anyhow::bail!("`chat_template` is not supported inside `chat_template_args`");
+    }
+    Ok(())
+}
+
 #[cfg(test)]
 mod tests {
     use std::collections::HashMap;
@@ -816,6 +829,23 @@ mod tests {
         HashMap::from([("experimental_field".to_string(), json!("value"))])
     }
 
+    #[test]
+    fn validate_chat_template_args_rejects_nested_chat_template() {
+        let args = HashMap::from([(
+            "chat_template".to_string(),
+            json!("{% for _ in range(10**9) %}x{% endfor %}"),
+        )]);
+        let err = validate_chat_template_args(Some(&args)).unwrap_err();
+        assert!(err.to_string().contains("chat_template"));
+    }
+
+    #[test]
+    fn validate_chat_template_args_accepts_other_keys() {
+        let args = HashMap::from([("enable_thinking".to_string(), json!(false))]);
+        validate_chat_template_args(Some(&args)).unwrap();
+        validate_chat_template_args(None).unwrap();
+    }
+
     #[test]
     fn validate_no_unsupported_fields_rejects_unknown_fields_by_default() {
         let err = validate_no_unsupported_fields_with_ignore(&unknown_fields(), false).unwrap_err();