diff --git a/codex-rs/core/src/network_proxy_loader.rs b/codex-rs/core/src/network_proxy_loader.rs
index 912073b1b4..a959faf4a5 100644
--- a/codex-rs/core/src/network_proxy_loader.rs
+++ b/codex-rs/core/src/network_proxy_loader.rs
@@ -178,6 +178,13 @@ fn apply_network_constraints(network: NetworkToml, constraints: &mut NetworkProx
     if let Some(allow_local_binding) = network.allow_local_binding {
         constraints.allow_local_binding = Some(allow_local_binding);
     }
+    if let Some(dangerously_allow_plaintext_credential_injection) = network
+        .mitm
+        .and_then(|mitm| mitm.dangerously_allow_plaintext_credential_injection)
+    {
+        constraints.dangerously_allow_plaintext_credential_injection =
+            Some(dangerously_allow_plaintext_credential_injection);
+    }
 }
 
 #[derive(Debug, Clone, Default, Deserialize)]
diff --git a/codex-rs/core/src/network_proxy_loader_tests.rs b/codex-rs/core/src/network_proxy_loader_tests.rs
index 879d826920..654329842c 100644
--- a/codex-rs/core/src/network_proxy_loader_tests.rs
+++ b/codex-rs/core/src/network_proxy_loader_tests.rs
@@ -214,6 +214,55 @@ dangerously_allow_plaintext_credential_injection = true
     );
 }
 
+#[test]
+fn managed_config_can_disable_plaintext_credential_injection() {
+    let managed_layer = ConfigLayerEntry::new(
+        ConfigLayerSource::System {
+            file: AbsolutePathBuf::try_from(std::path::PathBuf::from("/tmp/system.toml"))
+                .expect("system config path should be absolute"),
+        },
+        toml::toml! {
+            default_permissions = "workspace"
+
+            [permissions.workspace.network.mitm]
+            dangerously_allow_plaintext_credential_injection = false
+        }
+        .into(),
+    );
+    let user_layer = ConfigLayerEntry::new(
+        ConfigLayerSource::User {
+            file: AbsolutePathBuf::try_from(std::path::PathBuf::from("/tmp/config.toml"))
+                .expect("user config path should be absolute"),
+            profile: None,
+        },
+        toml::toml! {
+            [permissions.workspace.network.mitm]
+            dangerously_allow_plaintext_credential_injection = true
+        }
+        .into(),
+    );
+    let layers = ConfigLayerStack::new(
+        vec![managed_layer, user_layer],
+        ConfigRequirements::default(),
+        ConfigRequirementsToml::default(),
+    )
+    .expect("layer stack should be valid");
+    let config = config_from_layers(&layers, &Policy::empty())
+        .expect("merged network proxy config should load");
+
+    assert!(
+        config
+            .network
+            .dangerously_allow_plaintext_credential_injection
+    );
+    let err = enforce_trusted_constraints(&layers, &config)
+        .expect_err("managed config should disable plaintext credential injection");
+    assert_eq!(
+        format!("{err:#}"),
+        "network proxy constraints: invalid value for network.dangerously_allow_plaintext_credential_injection: true (allowed false (disabled by managed config))"
+    );
+}
+
 #[test]
 fn execpolicy_network_rules_overlay_network_lists() {
     let mut config = NetworkProxyConfig::default();
diff --git a/codex-rs/network-proxy/src/state.rs b/codex-rs/network-proxy/src/state.rs
index 9a5287dac4..024177895a 100644
--- a/codex-rs/network-proxy/src/state.rs
+++ b/codex-rs/network-proxy/src/state.rs
@@ -30,6 +30,7 @@ pub struct NetworkProxyConstraints {
     pub allow_upstream_proxy: Option<bool>,
     pub dangerously_allow_non_loopback_proxy: Option<bool>,
     pub dangerously_allow_all_unix_sockets: Option<bool>,
+    pub dangerously_allow_plaintext_credential_injection: Option<bool>,
     pub allowed_domains: Option<Vec<String>>,
     pub allowlist_expansion_enabled: Option<bool>,
     pub denied_domains: Option<Vec<String>>,
@@ -198,6 +199,27 @@ pub fn validate_policy_against_constraints(
         },
     )?;
 
+    if let Some(allow_plaintext_credential_injection) =
+        constraints.dangerously_allow_plaintext_credential_injection
+    {
+        validate(
+            config
+                .network
+                .dangerously_allow_plaintext_credential_injection,
+            move |candidate| {
+                if *candidate && !allow_plaintext_credential_injection {
+                    Err(invalid_value(
+                        "network.dangerously_allow_plaintext_credential_injection",
+                        "true",
+                        "false (disabled by managed config)",
+                    ))
+                } else {
+                    Ok(())
+                }
+            },
+        )?;
+    }
+
     let allow_all_unix_sockets = constraints
         .dangerously_allow_all_unix_sockets
         .unwrap_or(constraints.allow_unix_sockets.is_none());