diff --git a/Documentation/RelNotes/2.17.4.txt b/Documentation/RelNotes/2.17.4.txt
new file mode 100644
index 0000000..7d794ca
--- /dev/null
+++ b/Documentation/RelNotes/2.17.4.txt
@@ -0,0 +1,16 @@
+Git v2.17.4 Release Notes
+=========================
+
+This release is to address the security issue: CVE-2020-5260
+
+Fixes since v2.17.3
+-------------------
+
+ * With a crafted URL that contains a newline in it, the credential
+   helper machinery can be fooled to give credential information for
+   a wrong host.  The attack has been made impossible by forbidding
+   a newline character in any value passed via the credential
+   protocol.
+
+Credit for finding the vulnerability goes to Felix Wilhelm of Google
+Project Zero.
diff --git a/Documentation/RelNotes/2.18.3.txt b/Documentation/RelNotes/2.18.3.txt
new file mode 100644
index 0000000..25143f0
--- /dev/null
+++ b/Documentation/RelNotes/2.18.3.txt
@@ -0,0 +1,5 @@
+Git v2.18.3 Release Notes
+=========================
+
+This release merges the security fix that appears in v2.17.4; see
+the release notes for that version for details.
diff --git a/GIT-VERSION-GEN b/GIT-VERSION-GEN
index 5ae6419..fd9e5b8 100755
--- a/GIT-VERSION-GEN
+++ b/GIT-VERSION-GEN
@@ -1,7 +1,7 @@
 #!/bin/sh
 
 GVF=GIT-VERSION-FILE
-DEF_VER=v2.18.2
+DEF_VER=v2.18.3
 
 LF='
 '
diff --git a/RelNotes b/RelNotes
index 1b5f706..1811ee1 120000
--- a/RelNotes
+++ b/RelNotes
@@ -1 +1 @@
-Documentation/RelNotes/2.18.2.txt
\ No newline at end of file
+Documentation/RelNotes/2.18.3.txt
\ No newline at end of file
diff --git a/credential.c b/credential.c
index 62be651..2482382 100644
--- a/credential.c
+++ b/credential.c
@@ -195,6 +195,8 @@
 {
 	if (!value)
 		return;
+	if (strchr(value, '\n'))
+		die("credential value for %s contains newline", key);
 	fprintf(fp, "%s=%s\n", key, value);
 }
 
@@ -322,7 +324,22 @@
 	c->approved = 0;
 }
 
-void credential_from_url(struct credential *c, const char *url)
+static int check_url_component(const char *url, int quiet,
+			       const char *name, const char *value)
+{
+	if (!value)
+		return 0;
+	if (!strchr(value, '\n'))
+		return 0;
+
+	if (!quiet)
+		warning(_("url contains a newline in its %s component: %s"),
+			name, url);
+	return -1;
+}
+
+int credential_from_url_gently(struct credential *c, const char *url,
+			       int quiet)
 {
 	const char *at, *colon, *cp, *slash, *host, *proto_end;
 
@@ -336,7 +353,7 @@
 	 */
 	proto_end = strstr(url, "://");
 	if (!proto_end)
-		return;
+		return 0;
 	cp = proto_end + 3;
 	at = strchr(cp, '@');
 	colon = strchr(cp, ':');
@@ -371,4 +388,21 @@
 		while (p > c->path && *p == '/')
 			*p-- = '\0';
 	}
+
+	if (check_url_component(url, quiet, "username", c->username) < 0 ||
+	    check_url_component(url, quiet, "password", c->password) < 0 ||
+	    check_url_component(url, quiet, "protocol", c->protocol) < 0 ||
+	    check_url_component(url, quiet, "host", c->host) < 0 ||
+	    check_url_component(url, quiet, "path", c->path) < 0)
+		return -1;
+
+	return 0;
+}
+
+void credential_from_url(struct credential *c, const char *url)
+{
+	if (credential_from_url_gently(c, url, 0) < 0) {
+		warning(_("skipping credential lookup for url: %s"), url);
+		credential_clear(c);
+	}
 }
diff --git a/credential.h b/credential.h
index 6b0cd16..122a23c 100644
--- a/credential.h
+++ b/credential.h
@@ -28,7 +28,23 @@
 
 int credential_read(struct credential *, FILE *);
 void credential_write(const struct credential *, FILE *);
+
+/*
+ * Parse a url into a credential struct, replacing any existing contents.
+ *
+ * Ifthe url can't be parsed (e.g., a missing "proto://" component), the
+ * resulting credential will be empty but we'll still return success from the
+ * "gently" form.
+ *
+ * If we encounter a component which cannot be represented as a credential
+ * value (e.g., because it contains a newline), the "gently" form will return
+ * an error but leave the broken state in the credential object for further
+ * examination.  The non-gentle form will issue a warning to stderr and return
+ * an empty credential.
+ */
 void credential_from_url(struct credential *, const char *url);
+int credential_from_url_gently(struct credential *, const char *url, int quiet);
+
 int credential_match(const struct credential *have,
 		     const struct credential *want);
 
diff --git a/fsck.c b/fsck.c
index 6ccc638..55bd432 100644
--- a/fsck.c
+++ b/fsck.c
@@ -14,6 +14,7 @@
 #include "packfile.h"
 #include "submodule-config.h"
 #include "config.h"
+#include "credential.h"
 
 static struct oidset gitmodules_found = OIDSET_INIT;
 static struct oidset gitmodules_done = OIDSET_INIT;
@@ -945,6 +946,19 @@
 	return fsck_tag_buffer(tag, data, size, options);
 }
 
+static int check_submodule_url(const char *url)
+{
+	struct credential c = CREDENTIAL_INIT;
+	int ret;
+
+	if (looks_like_command_line_option(url))
+		return -1;
+
+	ret = credential_from_url_gently(&c, url, 1);
+	credential_clear(&c);
+	return ret;
+}
+
 struct fsck_gitmodules_data {
 	struct object *obj;
 	struct fsck_options *options;
@@ -969,7 +983,7 @@
 				    "disallowed submodule name: %s",
 				    name);
 	if (!strcmp(key, "url") && value &&
-	    looks_like_command_line_option(value))
+	    check_submodule_url(value) < 0)
 		data->ret |= report(data->options, data->obj,
 				    FSCK_MSG_GITMODULES_URL,
 				    "disallowed submodule url: %s",
diff --git a/t/lib-credential.sh b/t/lib-credential.sh
index 937b831..bb88cc0 100755
--- a/t/lib-credential.sh
+++ b/t/lib-credential.sh
@@ -19,7 +19,7 @@
 		false
 	fi &&
 	test_cmp expect-stdout stdout &&
-	test_cmp expect-stderr stderr
+	test_i18ncmp expect-stderr stderr
 }
 
 read_chunk() {
diff --git a/t/t0300-credentials.sh b/t/t0300-credentials.sh
index 03bd31e..3bec445 100755
--- a/t/t0300-credentials.sh
+++ b/t/t0300-credentials.sh
@@ -309,4 +309,18 @@
 	EOF
 '
 
+test_expect_success 'url parser ignores embedded newlines' '
+	check fill <<-EOF
+	url=https://one.example.com?%0ahost=two.example.com/
+	--
+	username=askpass-username
+	password=askpass-password
+	--
+	warning: url contains a newline in its host component: https://one.example.com?%0ahost=two.example.com/
+	warning: skipping credential lookup for url: https://one.example.com?%0ahost=two.example.com/
+	askpass: Username:
+	askpass: Password:
+	EOF
+'
+
 test_done
diff --git a/t/t7416-submodule-dash-url.sh b/t/t7416-submodule-dash-url.sh
index 5ba041f..41431b1 100755
--- a/t/t7416-submodule-dash-url.sh
+++ b/t/t7416-submodule-dash-url.sh
@@ -1,6 +1,6 @@
 #!/bin/sh
 
-test_description='check handling of .gitmodule url with dash'
+test_description='check handling of disallowed .gitmodule urls'
 . ./test-lib.sh
 
 test_expect_success 'create submodule with protected dash in url' '
@@ -60,4 +60,20 @@
 	test_i18ngrep ! "unknown option" err
 '
 
+test_expect_success 'fsck rejects embedded newline in url' '
+	# create an orphan branch to avoid existing .gitmodules objects
+	git checkout --orphan newline &&
+	cat >.gitmodules <<-\EOF &&
+	[submodule "foo"]
+	url = "https://one.example.com?%0ahost=two.example.com/foo.git"
+	EOF
+	git add .gitmodules &&
+	git commit -m "gitmodules with newline" &&
+	test_when_finished "rm -rf dst" &&
+	git init --bare dst &&
+	git -C dst config transfer.fsckObjects true &&
+	test_must_fail git push dst HEAD 2>err &&
+	grep gitmodulesUrl err
+'
+
 test_done