diff --git a/doc/manual/rl-next/verify-tls.md b/doc/manual/rl-next/verify-tls.md
new file mode 100644
index 00000000000..afc689f46a9
--- /dev/null
+++ b/doc/manual/rl-next/verify-tls.md
@@ -0,0 +1,8 @@
+---
+synopsis: "`<nix/fetchurl.nix>` uses TLS verification"
+prs: [11585]
+---
+
+Previously `<nix/fetchurl.nix>` did not do TLS verification. This was because the Nix sandbox in the past did not have access to TLS certificates, and Nix checks the hash of the fetched file anyway. However, this can expose authentication data from `netrc` and URLs to man-in-the-middle attackers. In addition, Nix now in some cases (such as when using impure derivations) does *not* check the hash. Therefore we have now enabled TLS verification. This means that downloads by `<nix/fetchurl.nix>` will now fail if you're fetching from a HTTPS server that does not have a valid certificate.
+
+`<nix/fetchurl.nix>` is also known as the builtin derivation builder `builtin:fetchurl`. It's not to be confused with the evaluation-time function `builtins.fetchurl`, which was not affected by this issue.
diff --git a/src/libstore/builtins/fetchurl.cc b/src/libstore/builtins/fetchurl.cc
index b9dfeba2f8e..f33060c3307 100644
--- a/src/libstore/builtins/fetchurl.cc
+++ b/src/libstore/builtins/fetchurl.cc
@@ -38,10 +38,7 @@ void builtinFetchurl(
 
         auto source = sinkToSource([&](Sink & sink) {
 
-            /* No need to do TLS verification, because we check the hash of
-               the result anyway. */
             FileTransferRequest request(url);
-            request.verifyTLS = false;
             request.decompress = false;
 
             auto decompressor = makeDecompressionSink(
diff --git a/tests/nixos/default.nix b/tests/nixos/default.nix
index afcc07ea617..c5b0f68f1b6 100644
--- a/tests/nixos/default.nix
+++ b/tests/nixos/default.nix
@@ -164,4 +164,6 @@ in
   gzip-content-encoding = runNixOSTestFor "x86_64-linux" ./gzip-content-encoding.nix;
 
   user-sandboxing = runNixOSTestFor "x86_64-linux" ./user-sandboxing;
+
+  fetchurl = runNixOSTestFor "x86_64-linux" ./fetchurl.nix;
 }
diff --git a/tests/nixos/fetchurl.nix b/tests/nixos/fetchurl.nix
new file mode 100644
index 00000000000..476f779bcc3
--- /dev/null
+++ b/tests/nixos/fetchurl.nix
@@ -0,0 +1,78 @@
+# Test whether builtin:fetchurl properly performs TLS certificate
+# checks on HTTPS servers.
+
+{ lib, config, pkgs, ... }:
+
+let
+
+  makeTlsCert = name: pkgs.runCommand name {
+    nativeBuildInputs = with pkgs; [ openssl ];
+  } ''
+    mkdir -p $out
+    openssl req -x509 \
+      -subj '/CN=${name}/' -days 49710 \
+      -addext 'subjectAltName = DNS:${name}' \
+      -keyout "$out/key.pem" -newkey ed25519 \
+      -out "$out/cert.pem" -noenc
+  '';
+
+  goodCert = makeTlsCert "good";
+  badCert = makeTlsCert "bad";
+
+in
+
+{
+  name = "nss-preload";
+
+  nodes = {
+    machine = { lib, pkgs, ... }: {
+      services.nginx = {
+        enable = true;
+
+        virtualHosts."good" = {
+          addSSL = true;
+          sslCertificate = "${goodCert}/cert.pem";
+          sslCertificateKey = "${goodCert}/key.pem";
+          root = pkgs.runCommand "nginx-root" {} ''
+            mkdir "$out"
+            echo 'hello world' > "$out/index.html"
+          '';
+        };
+
+        virtualHosts."bad" = {
+          addSSL = true;
+          sslCertificate = "${badCert}/cert.pem";
+          sslCertificateKey = "${badCert}/key.pem";
+          root = pkgs.runCommand "nginx-root" {} ''
+            mkdir "$out"
+            echo 'foobar' > "$out/index.html"
+          '';
+        };
+      };
+
+      security.pki.certificateFiles = [ "${goodCert}/cert.pem" ];
+
+      networking.hosts."127.0.0.1" = [ "good" "bad" ];
+
+      virtualisation.writableStore = true;
+
+      nix.settings.experimental-features = "nix-command";
+    };
+  };
+
+  testScript = { nodes, ... }: ''
+    machine.wait_for_unit("nginx")
+    machine.wait_for_open_port(443)
+
+    out = machine.succeed("curl https://good/index.html")
+    assert out == "hello world\n"
+
+    # Fetching from a server with a trusted cert should work.
+    machine.succeed("nix build --no-substitute --expr 'import <nix/fetchurl.nix> { url = \"https://good/index.html\"; hash = \"sha256-qUiQTy8PR5uPgZdpSzAYSw0u0cHNKh7A+4XSmaGSpEc=\"; }'")
+
+    # Fetching from a server with an untrusted cert should fail.
+    err = machine.fail("nix build --no-substitute --expr 'import <nix/fetchurl.nix> { url = \"https://bad/index.html\"; hash = \"sha256-rsBwZF/lPuOzdjBZN2E08FjMM3JHyXit0Xi2zN+wAZ8=\"; }' 2>&1")
+    print(err)
+    assert "SSL certificate problem: self-signed certificate" in err
+  '';
+}