diff --git a/Documentation/RelNotes/2.17.4.txt b/Documentation/RelNotes/2.17.4.txt
new file mode 100644
index 00000000000000..7d794ca01af216
--- /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 00000000000000..25143f0cec5804
--- /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/Documentation/RelNotes/2.19.4.txt b/Documentation/RelNotes/2.19.4.txt
new file mode 100644
index 00000000000000..35d0ae561b6faf
--- /dev/null
+++ b/Documentation/RelNotes/2.19.4.txt
@@ -0,0 +1,5 @@
+Git v2.19.4 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/Documentation/RelNotes/2.20.3.txt b/Documentation/RelNotes/2.20.3.txt
new file mode 100644
index 00000000000000..f6eccd103b6966
--- /dev/null
+++ b/Documentation/RelNotes/2.20.3.txt
@@ -0,0 +1,5 @@
+Git v2.20.3 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/Documentation/RelNotes/2.21.2.txt b/Documentation/RelNotes/2.21.2.txt
new file mode 100644
index 00000000000000..a0fb83bb534104
--- /dev/null
+++ b/Documentation/RelNotes/2.21.2.txt
@@ -0,0 +1,5 @@
+Git v2.21.2 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/Documentation/RelNotes/2.22.3.txt b/Documentation/RelNotes/2.22.3.txt
new file mode 100644
index 00000000000000..57296f6d173f70
--- /dev/null
+++ b/Documentation/RelNotes/2.22.3.txt
@@ -0,0 +1,5 @@
+Git v2.22.3 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/Documentation/RelNotes/2.23.2.txt b/Documentation/RelNotes/2.23.2.txt
new file mode 100644
index 00000000000000..b697cbe0e31a0b
--- /dev/null
+++ b/Documentation/RelNotes/2.23.2.txt
@@ -0,0 +1,5 @@
+Git v2.23.2 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/Documentation/RelNotes/2.24.2.txt b/Documentation/RelNotes/2.24.2.txt
new file mode 100644
index 00000000000000..0049f65503eb86
--- /dev/null
+++ b/Documentation/RelNotes/2.24.2.txt
@@ -0,0 +1,5 @@
+Git v2.24.2 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/Documentation/RelNotes/2.25.3.txt b/Documentation/RelNotes/2.25.3.txt
new file mode 100644
index 00000000000000..15f7f21f1002e9
--- /dev/null
+++ b/Documentation/RelNotes/2.25.3.txt
@@ -0,0 +1,5 @@
+Git v2.25.3 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/Documentation/RelNotes/2.26.1.txt b/Documentation/RelNotes/2.26.1.txt
new file mode 100644
index 00000000000000..1b4ecb3fdc5473
--- /dev/null
+++ b/Documentation/RelNotes/2.26.1.txt
@@ -0,0 +1,5 @@
+Git v2.26.1 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/credential.c b/credential.c
index 77dfde44e3d136..21b3ba152fe23f 100644
--- a/credential.c
+++ b/credential.c
@@ -226,6 +226,8 @@ static void credential_write_item(FILE *fp, const char *key, const char *value)
 {
 	if (!value)
 		return;
+	if (strchr(value, '\n'))
+		die("credential value for %s contains newline", key);
 	fprintf(fp, "%s=%s\n", key, value);
 }
 
@@ -353,7 +355,22 @@ void credential_reject(struct credential *c)
 	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;
 
@@ -367,7 +384,7 @@ void credential_from_url(struct credential *c, const char *url)
 	 */
 	proto_end = strstr(url, "://");
 	if (!proto_end)
-		return;
+		return 0;
 	cp = proto_end + 3;
 	at = strchr(cp, '@');
 	colon = strchr(cp, ':');
@@ -406,4 +423,21 @@ void credential_from_url(struct credential *c, const char *url)
 		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 fec7815dd0d60b..d99ec42b2a8c96 100644
--- a/credential.h
+++ b/credential.h
@@ -173,8 +173,21 @@ void credential_reject(struct credential *);
 int credential_read(struct credential *, FILE *);
 void credential_write(const struct credential *, FILE *);
 
-/* Parse a URL into broken-down credential fields. */
+/*
+ * Parse a url into a credential struct, replacing any existing contents.
+ *
+ * If the 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 640d813d8430c6..dc6f6ac3de193d 100644
--- a/fsck.c
+++ b/fsck.c
@@ -15,6 +15,7 @@
 #include "packfile.h"
 #include "submodule-config.h"
 #include "config.h"
+#include "credential.h"
 #include "help.h"
 
 static struct oidset gitmodules_found = OIDSET_INIT;
@@ -910,6 +911,19 @@ static int fsck_tag(const struct object_id *oid, const char *buffer,
 	return ret;
 }
 
+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 {
 	const struct object_id *oid;
 	struct fsck_options *options;
@@ -935,7 +949,7 @@ static int fsck_gitmodules_fn(const char *var, const char *value, void *vdata)
 				    "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->oid, OBJ_BLOB,
 				    FSCK_MSG_GITMODULES_URL,
diff --git a/t/lib-credential.sh b/t/lib-credential.sh
index 937b831ea67523..bb88cc01087ba1 100755
--- a/t/lib-credential.sh
+++ b/t/lib-credential.sh
@@ -19,7 +19,7 @@ check() {
 		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 39f097ea9e5094..5b78ebbc3f2235 100755
--- a/t/t0300-credentials.sh
+++ b/t/t0300-credentials.sh
@@ -436,4 +436,18 @@ test_expect_success 'empty helper spec resets helper list' '
 	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 5ba041f537067d..41431b1ac38e5c 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_expect_success 'trailing backslash is handled correctly' '
 	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