From 7725b8100ffbbff2750ee4d61a0fcc1f53a086e8 Mon Sep 17 00:00:00 2001 From: Johannes Schindelin Date: Wed, 30 Oct 2024 13:26:10 +0100 Subject: credential: sanitize the user prompt When asking the user interactively for credentials, we want to avoid misleading them e.g. via control sequences that pretend that the URL targets a trusted host when it does not. While Git learned, over the course of the preceding commits, to disallow URLs containing URL-encoded control characters by default, credential helpers are still allowed to specify values very freely (apart from Line Feed and NUL characters, anything is allowed), and this would allow, say, a username containing control characters to be specified that would then be displayed in the interactive terminal prompt asking the user for the password, potentially sending those control characters directly to the terminal. This is undesirable because control characters can be used to mislead users to divulge secret information to untrusted sites. To prevent such an attack vector, let's add a `git_prompt()` that forces the displayed text to be sanitized, i.e. displaying question marks instead of control characters. Note: While this commit's diff changes a lot of `user@host` strings to `user%40host`, which may look suspicious on the surface, there is a good reason for that: this string specifies a user name, not a @ combination! In the context of t5541, the actual combination looks like this: `user%40@127.0.0.1:5541`. Therefore, these string replacements document a net improvement introduced by this commit, as `user@host@127.0.0.1` could have left readers wondering where the user name ends and where the host name begins. Hinted-at-by: Jeff King Signed-off-by: Johannes Schindelin --- credential.h | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) (limited to 'credential.h') diff --git a/credential.h b/credential.h index 935b28a70f..0364d436d2 100644 --- a/credential.h +++ b/credential.h @@ -119,7 +119,8 @@ struct credential { configured:1, quit:1, use_http_path:1, - username_from_proto:1; + username_from_proto:1, + sanitize_prompt:1; char *username; char *password; @@ -132,6 +133,7 @@ struct credential { #define CREDENTIAL_INIT { \ .helpers = STRING_LIST_INIT_DUP, \ .password_expiry_utc = TIME_MAX, \ + .sanitize_prompt = 1, \ } /* Initialize a credential structure, setting all fields to empty. */ -- cgit 1.2.3-korg From b01b9b81d36759cdcd07305e78765199e1bc2060 Mon Sep 17 00:00:00 2001 From: Johannes Schindelin Date: Mon, 4 Nov 2024 14:48:22 +0100 Subject: credential: disallow Carriage Returns in the protocol by default While Git has documented that the credential protocol is line-based, with newlines as terminators, the exact shape of a newline has not been documented. From Git's perspective, which is firmly rooted in the Linux ecosystem, it is clear that "a newline" means a Line Feed character. However, even Git's credential protocol respects Windows line endings (a Carriage Return character followed by a Line Feed character, "CR/LF") by virtue of using `strbuf_getline()`. There is a third category of line endings that has been used originally by MacOS, and that is respected by the default line readers of .NET and node.js: bare Carriage Returns. Git cannot handle those, and what is worse: Git's remedy against CVE-2020-5260 does not catch when credential helpers are used that interpret bare Carriage Returns as newlines. Git Credential Manager addressed this as CVE-2024-50338, but other credential helpers may still be vulnerable. So let's not only disallow Line Feed characters as part of the values in the credential protocol, but also disallow Carriage Return characters. In the unlikely event that a credential helper relies on Carriage Returns in the protocol, introduce an escape hatch via the `credential.protectProtocol` config setting. This addresses CVE-2024-52006. Signed-off-by: Johannes Schindelin --- Documentation/config/credential.txt | 5 +++++ credential.c | 21 ++++++++++++++------- credential.h | 4 +++- t/t0300-credentials.sh | 16 ++++++++++++++++ 4 files changed, 38 insertions(+), 8 deletions(-) (limited to 'credential.h') diff --git a/Documentation/config/credential.txt b/Documentation/config/credential.txt index fd8113d6d4..9cadca7f73 100644 --- a/Documentation/config/credential.txt +++ b/Documentation/config/credential.txt @@ -20,6 +20,11 @@ credential.sanitizePrompt:: will be URL-encoded by default). Configure this setting to `false` to override that behavior. +credential.protectProtocol:: + By default, Carriage Return characters are not allowed in the protocol + that is used when Git talks to a credential helper. This setting allows + users to override this default. + credential.username:: If no username is set for a network authentication, use this username by default. See credential..* below, and diff --git a/credential.c b/credential.c index 1392a54d5c..b76a730901 100644 --- a/credential.c +++ b/credential.c @@ -69,6 +69,8 @@ static int credential_config_callback(const char *var, const char *value, c->use_http_path = git_config_bool(var, value); else if (!strcmp(key, "sanitizeprompt")) c->sanitize_prompt = git_config_bool(var, value); + else if (!strcmp(key, "protectprotocol")) + c->protect_protocol = git_config_bool(var, value); return 0; } @@ -262,7 +264,8 @@ int credential_read(struct credential *c, FILE *fp) return 0; } -static void credential_write_item(FILE *fp, const char *key, const char *value, +static void credential_write_item(const struct credential *c, + FILE *fp, const char *key, const char *value, int required) { if (!value && required) @@ -271,19 +274,23 @@ static void credential_write_item(FILE *fp, const char *key, const char *value, return; if (strchr(value, '\n')) die("credential value for %s contains newline", key); + if (c->protect_protocol && strchr(value, '\r')) + die("credential value for %s contains carriage return\n" + "If this is intended, set `credential.protectProtocol=false`", + key); fprintf(fp, "%s=%s\n", key, value); } void credential_write(const struct credential *c, FILE *fp) { - credential_write_item(fp, "protocol", c->protocol, 1); - credential_write_item(fp, "host", c->host, 1); - credential_write_item(fp, "path", c->path, 0); - credential_write_item(fp, "username", c->username, 0); - credential_write_item(fp, "password", c->password, 0); + credential_write_item(c, fp, "protocol", c->protocol, 1); + credential_write_item(c, fp, "host", c->host, 1); + credential_write_item(c, fp, "path", c->path, 0); + credential_write_item(c, fp, "username", c->username, 0); + credential_write_item(c, fp, "password", c->password, 0); if (c->password_expiry_utc != TIME_MAX) { char *s = xstrfmt("%"PRItime, c->password_expiry_utc); - credential_write_item(fp, "password_expiry_utc", s, 0); + credential_write_item(c, fp, "password_expiry_utc", s, 0); free(s); } } diff --git a/credential.h b/credential.h index 0364d436d2..2c0b39a925 100644 --- a/credential.h +++ b/credential.h @@ -120,7 +120,8 @@ struct credential { quit:1, use_http_path:1, username_from_proto:1, - sanitize_prompt:1; + sanitize_prompt:1, + protect_protocol:1; char *username; char *password; @@ -134,6 +135,7 @@ struct credential { .helpers = STRING_LIST_INIT_DUP, \ .password_expiry_utc = TIME_MAX, \ .sanitize_prompt = 1, \ + .protect_protocol = 1, \ } /* Initialize a credential structure, setting all fields to empty. */ diff --git a/t/t0300-credentials.sh b/t/t0300-credentials.sh index b62c70c193..168ae76550 100755 --- a/t/t0300-credentials.sh +++ b/t/t0300-credentials.sh @@ -720,6 +720,22 @@ test_expect_success 'url parser rejects embedded newlines' ' test_cmp expect stderr ' +test_expect_success 'url parser rejects embedded carriage returns' ' + test_config credential.helper "!true" && + test_must_fail git credential fill 2>stderr <<-\EOF && + url=https://example%0d.com/ + EOF + cat >expect <<-\EOF && + fatal: credential value for host contains carriage return + If this is intended, set `credential.protectProtocol=false` + EOF + test_cmp expect stderr && + GIT_ASKPASS=true \ + git -c credential.protectProtocol=false credential fill <<-\EOF + url=https://example%0d.com/ + EOF +' + test_expect_success 'host-less URLs are parsed as empty host' ' check fill "verbatim foo bar" <<-\EOF url=cert:///path/to/cert.pem -- cgit 1.2.3-korg