From 635e2a8b337ffff6e64a27b722c4cd332752af1f Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Micha=C3=ABl=20Zasso?= <targos@protonmail.com>
Date: Wed, 14 Jun 2017 10:46:50 +0200
Subject: [PATCH 1/2] util: ignore invalid format specifiers

In util.format, if a percent sign without a known type is encountered,
just print it instead of silently ignoring it and the next character.

Fixes: https://github.com/nodejs/node/issues/13665
---
 lib/util.js                       | 6 ++++++
 test/parallel/test-util-format.js | 5 +++++
 2 files changed, 11 insertions(+)

diff --git a/lib/util.js b/lib/util.js
index 921a684d50c2fb..4f6d727eaa7391 100644
--- a/lib/util.js
+++ b/lib/util.js
@@ -113,6 +113,12 @@ exports.format = function(f) {
             str += f.slice(lastPos, i);
           str += '%';
           break;
+        default: // any other character is not a correct placeholder
+          if (lastPos < i)
+            str += f.slice(lastPos, i);
+          str += '%';
+          lastPos = i = i + 1;
+          continue;
       }
       lastPos = i = i + 2;
       continue;
diff --git a/test/parallel/test-util-format.js b/test/parallel/test-util-format.js
index 93998c598a0e1f..1b4a40eaf9b6ec 100644
--- a/test/parallel/test-util-format.js
+++ b/test/parallel/test-util-format.js
@@ -126,6 +126,11 @@ assert.strictEqual(util.format('o: %j, a: %j', {}, []), 'o: {}, a: []');
 assert.strictEqual(util.format('o: %j, a: %j', {}), 'o: {}, a: %j');
 assert.strictEqual(util.format('o: %j, a: %j'), 'o: %j, a: %j');
 
+// Invalid format specifiers
+assert.strictEqual(util.format('a% b', 'x'), 'a% b x');
+assert.strictEqual(util.format('percent: %d%, fraction: %d', 10, 0.1),
+                   'percent: 10%, fraction: 0.1');
+
 {
   const o = {};
   o.o = o;

From e8198c4213379815d23f4b0e725a04dd79d8bbbb Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Micha=C3=ABl=20Zasso?= <targos@protonmail.com>
Date: Wed, 14 Jun 2017 11:46:25 +0200
Subject: [PATCH 2/2] fixup: add test with % at the end

---
 test/parallel/test-util-format.js | 1 +
 1 file changed, 1 insertion(+)

diff --git a/test/parallel/test-util-format.js b/test/parallel/test-util-format.js
index 1b4a40eaf9b6ec..084e6f73b90ddf 100644
--- a/test/parallel/test-util-format.js
+++ b/test/parallel/test-util-format.js
@@ -130,6 +130,7 @@ assert.strictEqual(util.format('o: %j, a: %j'), 'o: %j, a: %j');
 assert.strictEqual(util.format('a% b', 'x'), 'a% b x');
 assert.strictEqual(util.format('percent: %d%, fraction: %d', 10, 0.1),
                    'percent: 10%, fraction: 0.1');
+assert.strictEqual(util.format('abc%', 1), 'abc% 1');
 
 {
   const o = {};