Message-ID: Date: Sat, 15 Feb 2025 11:42:13 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird From: phoebe To: shuduizhang@xiaohongshu.com Content-Language: en-US Autocrypt: addr=phoebe@flowerfield.dev; keydata= xjMEZxO/yBYJKwYBBAHaRw8BAQdAlagvf+uRL4Ug5npHaABJElUWLw5OxRF9r8VmqCBus8jN JVBob2ViZSBEdXNpbCA8cGhvZWJlQGZsb3dlcmZpZWxkLmRldj7CmQQTFgoAQQIbAwULCQgH AgIiAgYVCgkICwIEFgIDAQIeBwIXgBYhBDxqjXxo2Rs9dKIdc5swI71KOSQ7BQJnGDqABQkF qBU4AAoJEJswI71KOSQ7qOYA/jWtLOmqsCA0eqjpH20n4d/5Yi/ab4ACyA13HUsYjpbtAPsH c+AAJGYpo8kJWmdVWHBegvagd/QPGpSeN5IPLlFuB844BGcTv8gSCisGAQQBl1UBBQEBB0BM 7hwvFDz/OnEqGtlehnwqDSbGrmBBAMlCnQoilCVnMQMBCAfCeAQYFgoAIBYhBDxqjXxo2Rs9 dKIdc5swI71KOSQ7BQJnE7/IAhsMAAoJEJswI71KOSQ7dyEA/11Oas2mCaz08I6CvqDcx2Ej ecPtqVyTqnvuXM3NQPslAP42xdh6Rcx6l7mwivWmnRAfg4yf5x0h/rUIXEkt+rntDw== Subject: Critical network vulnerability Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="------------81Crbut4NxK0WJp0kz00yQp0" This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --------------81Crbut4NxK0WJp0kz00yQp0 Content-Type: multipart/mixed; boundary="------------FDXySm3eSRGq0eQWzxiUgbuc"; protected-headers="v1" From: phoebe To: shuduizhang@xiaohongshu.com Message-ID: Subject: Critical network vulnerability --------------FDXySm3eSRGq0eQWzxiUgbuc Content-Type: multipart/mixed; boundary="------------m4C2lQ9CEb1Ql6Roklxoxecl" --------------m4C2lQ9CEb1Ql6Roklxoxecl Content-Type: multipart/alternative; boundary="------------fNf0i7ksF6iR3RXpy3OKuavz" --------------fNf0i7ksF6iR3RXpy3OKuavz Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: base64 RGVhciBYaWFvaG9uZ3NodSB0ZWFtLA0KDQpteSBuYW1lIGlzIFBob2ViZSBhbmQgSSBhbSBh IHNlY3VyaXR5IHJlc2VhcmNoZXIuIEZvciB0aGUgcGFzdCB3ZWVrIEkgDQpoYXZlIGJlZW4g bG9va2luZyBpbnRvIHRoZSBSZWROb3RlIGFwcCBhbmQgZGlzY292ZXJlZCBzZXZlcmUgaXNz dWVzIGluIA0KaG93IHRoZSBhcHAgaW50ZXJhY3RzIHdpdGggdGhlIHNlcnZlciBBUEkuDQoN Cg0KICAgICAgVGVjaG5pY2FsIGRldGFpbHMNCg0KUGFydCBvZiB0aGUgbmV0d29yayBjb21t dW5pY2F0aW9uIGluIHRoZSBSZWROb3RlIGFwcCAoY29tLnhpbmdpbi54aHMpIGlzIA0KdW5l bmNyeXB0ZWQgYWxsb3dpbmcgYWR2ZXJzYXJpZXMgdG8gbGlzdGVuIHRvIHRoZSBuZXR3b3Jr IGFuZCBjYXB0dXJlIA0KaW5mb3JtYXRpb24gYWJvdXQgdGhlIHVzZXIuIFRoaXMgaW5mb3Jt YXRpb24gaW5jbHVkZXMgd2hhdCBhY3Rpb25zIHRoZSANCnVzZXIgcGVyZm9ybXMgb24geW91 ciBzZXJ2aWNlIChmb2xsb3dpbmcgYWNjb3VudHMsIGxpa2luZyBwb3N0cywgc2VuZGluZyAN CmRpcmVjdCBtZXNzYWdlcywgZXRjLiksIGJ1dCBhbHNvIGluZm9ybWF0aW9uIGFib3V0IHRo ZSBkZXZpY2UgdGhlIHVzZXIgDQppcyBsb2dnaW5nIGludG8gdGhlIGFwcCBvbi4gQWxsIG9m IHRoaXMgaGFwcGVucyBpbiB0aGUgbGlieGhzbG9uZ2xpbmsuc28gDQpzaGFyZWQgbGlicmFy eSwgd2hlcmUgaXQgY3JlYXRlcyBhIGNvbm5lY3Rpb24gdG8gb25lIG9mIHRoZSBzZXJ2ZXIg SVBzIA0Kb3ZlciBwb3J0IDUzMzMgYW5kIHNlbmRzIHBhY2tldHMgY29udGFpbmluZyBhIDEy IGJ5dGUgaGVhZGVyIGFuZCBhIA0KcHJvdG9idWYtZW5jb2RlZCBwYXlsb2FkLg0KDQpTb21l IG9mIHRoZSBwYXlsb2FkcyBkbyBub3QgbGVhayB0b28gbXVjaCBpbmZvcm1hdGlvbiwgYnV0 IGV2ZW4ganVzdCBpbiANCnRoZSBmaXJzdCBjb3VwbGUgb2YgcGFja2V0cyBhIFNlc3Npb25B dXRoIHByb3RvIG1lc3NhZ2UgaXMgc2VudCBhbmQgYW4gDQpBdXRoUmVzcCBtZXNzYWdlIGlz IHJldHVybmVkIGJ5IHRoZSBzZXJ2ZXIuIElmIGFuIGFkdmVyc2FyeSwgd2hvIHdlIHdpbGwg DQpjYWxsIEV2ZSwgY2FwdHVyZXMgdGhlIFNlc3Npb25BdXRoIG9mIGEgdXNlciBBbGljZSwg RXZlIGNhbiB0aGVuIHNhdmUgDQpBbGljZSdzIGF1dGhlbnRpY2F0aW9uIGluZm9ybWF0aW9u IGFuZCBhdCBhIGxhdGVyIHBvaW50IGluIHRpbWUgDQphdXRoZW50aWNhdGUgYXMgQWxpY2Ug aW4gdGhlIEFQSSBhbmQgcGVyZm9ybSBvdGhlciBBUEkgYWN0aW9ucyB0aHJvdWdoIA0KQWxp Y2UncyBhY2NvdW50LiBFc3NlbnRpYWxseSBnaXZpbmcgRXZlIGNvbXBsZXRlIGNvbnRyb2wg b3ZlciBBbGljZSdzIA0KYWNjb3VudC4NCg0KSW4gc29tZSBjYXNlcyB0aGUgU2Vzc2lvbkF1 dGggd2lsbCBoYXZlIGEgY2lwaGVyVHlwZSBmaWVsZCBzZXQgdG8gMSwgDQpjYXVzaW5nIGNo YXQgcHJvdG8gbWVzc2FnZXMgdG8gYmUgZW5jcnlwdGVkIHVzaW5nIEFFUzEyOC1FQ0IsIGJ1 dCB0aGUgDQprZXkgdXNlZCBmb3IgdGhlIGVuY3J5cHRpb24gaXMgYWxzbyBzZW50IGluIHBs YWludGV4dCBpbiB0aGUgQXV0aFJlc3AsIA0KdGh1cyBhbGxvd2luZyBFdmUgdG8gY2FwdHVy ZSB0aGUga2V5IGFuZCBkZWNyeXB0IGFsbCBzdWNoIHBhY2tldHMgYXMgd2VsbC4NCg0KQXMg YW4gYWRkaXRpb25hbCBpc3N1ZSwgdGhlIG9ubHkgaW5mb3JtYXRpb24gbmVjZXNzYXJ5IHRv IGdldCANCmF1dGhlbnRpY2F0ZWQgd2l0aCB0aGUgc2VydmVyIGlzIGEgdWlkLCBhbiBzaWQg KHRva2VuKSBhbmQgZGV2aWNlIA0KaW5mb3JtYXRpb24uIENvbnNpZGVyaW5nIHRoZSB1aWQg aXMgcHVibGljIGluZm9ybWF0aW9uIGFuZCB0aGUgc2lkIGxvb2tzIA0KdG8gYmUgYSBuYW5v c2Vjb25kIHRpbWVzdGFtcCBvZiBhY2NvdW50IGNyZWF0aW9uIHdpdGggc29tZSBleHRyYSBk aWdpdHMsIA0KdGhpcyBsZWF2ZXMgYWJvdXQgNiBkaWdpdHMgKGFzc3VtaW5nIHRoZSBuYW5v c2Vjb25kIHByZWNpc2lvbiBpcyANCmRpZmZpY3VsdCB0byBmaW5kKSBvZiBzZWN1cml0eSBh bmQgZGV2aWNlIGluZm9ybWF0aW9uIGtlZXBpbmcgYW4gYWNjb3VudCANCnNlY3VyZSwgd2hp Y2ggaW4gaXRzZWxmIGlzIGNvbmNlcm5pbmcgYW5kIHNob3VsZCBiZSBoYXJkZW5lZC4NCg0K DQogICAgICBTb2x1dGlvbnMNCg0KVGhlIGFwcCBpcyBjYXBhYmxlIG9mIHVzaW5nIFRMUyBm b3IgY29tbXVuaWNhdGluZyB3aXRoIHRoZSBDRE5zLCBzbyBJIA0Kd291bGQgc3VnZ2VzdCBt aWdyYXRpbmcgdGhlIGNvbnRyb2wgQVBJIHRvIHVzaW5nIFRMUy4gVXNpbmcgYSANCnByb3By aWV0YXJ5IHByb3RvY29sIHVzdWFsbHkgc291bmRzIGxpa2UgYSBuaWNlIGlkZWEsIGJ1dCB1 bHRpbWF0ZWx5IA0KZmFpbHMgaW4gcHJhY3RpY2UsIHNvIEkgY2Fubm90IHN0cmVzcyBlbm91 Z2ggaG93IGltcG9ydGFudCBpdCBpcyB0byANCm1pZ3JhdGUgdG8gcHJvdG9jb2xzIHRoYXQg aGF2ZSBiZWVuIHNjcnV0aW5pemVkIGluIHRoZSBwYXN0Lg0KDQpDb25zaWRlcmluZyB0aGUg c2V2ZXJpdHkgb2YgdGhlIHZ1bG5lcmFiaWxpdHkgaXQgd291bGQgYmUgcmVzcG9uc2libGUg dG8gDQppbnRyb2R1Y2UgYSBicmVha2luZyBjaGFuZ2UgYW5kIGZvcmNlIHVzZXJzIHRvIHVw ZGF0ZSBpbnN0ZWFkIG9mIA0KZ3JhZHVhbGx5IG1pZ3JhdGluZyB0aGUgQVBJcywgc2luY2Ug YSB0cmFuc2l0aW9uIHBoYXNlIHdvdWxkIGFsbG93IA0KYWR2ZXJzYXJpZXMgdG8gY29sbGVj dCBhcyBtdWNoIGluZm9ybWF0aW9uIGFib3V0IHlvdXIgdXNlcnMgYXMgdGhleSBjYW4gDQp3 aGlsZSB0aGUgbWlncmF0aW9uIGhhcHBlbnMuDQoNCkFzIGZvciB0aGUgaXNzdWUgd2l0aCBv bmx5IG5lZWRpbmcgYSB0aW1lc3RhbXAtZm9ybWVkIHNpZCBhbmQgZGV2aWNlIA0KaW5mb3Jt YXRpb24gdG8gbG9naW4gdG8gYW4gYWNjb3VudCwgaXQgaXMgbmVjZXNzYXJ5IHRoYXQgeW91 IGltcHJvdmUgdGhlIA0Kc2VjdXJpdHkgb2YgYWNjb3VudHMgYW5kIGludHJvZHVjZSBlLmcu IGEgcGFzc3dvcmQgc2NoZW1lIHVzaW5nIGhhc2hlZCANCnBhc3N3b3JkIHN0cmluZ3MsIG9y IG90aGVyIHNpbWlsYXIgc2NoZW1lcyB0aGF0IHVzZSBpbmZvcm1hdGlvbiBvbmx5IA0Ka25v d24gYnkgdGhlIGFjY291bnQgaG9sZGVyIGFuZCB0aGF0IGNhbm5vdCBiZSBndWVzc2VkIGJh c2VkIG9uIA0Kb2JzZXJ2YWJsZSBpbmZvcm1hdGlvbi4NCg0KDQogICAgICBQdWJsaWNhdGlv bg0KDQpUaGUgdnVsbmVyYWJpbGl0aWVzIEkgYW0gYnJpbmdpbmcgdG8geW91ciBhdHRlbnRp b24gaW4gdGhpcyBlbWFpbCB3aWxsIA0KYmUgcHVibGljaXplZCBieSB0aGUgZW5kIG9mIG5l eHQgd2VlayAodGhlIDIzcmQgb2YgRmVicnVhcnkpLCBldmVuIGlmIA0Kbm90IHlldCBmaXhl ZC4gQWx0aG91Z2gsIEkgZG8gdW5kZXJzdGFuZCB1cGRhdGluZyBjb2RlIHRha2VzIHRpbWUg YW5kIA0KZWZmb3J0LCBzbyBpZiB5b3Ugd2lzaCBmb3IgbWUgdG8gZGVsYXkgYnJpbmdpbmcg dGhpcyBpc3N1ZSB0byB0aGUgDQpwdWJsaWMsIGZlZWwgZnJlZSB0byByZWFjaCBvdXQgYW5k IHdlIGNhbiBkaXNjdXNzIHNwZWNpZmljcy4NCg0KSW4gdGhlIGVuZCwgbXkgbWFpbiBwcmlv cml0eSBpcyB0aGUgc2VjdXJpdHkgb2YgeW91ciB1c2Vycywgc28gSSBhbSBvcGVuIA0KdG8g YW55IHF1ZXN0aW9ucyB5b3VyIHRlYW0gbWF5IGhhdmUuDQoNCg0KS2luZGVzdCByZWdhcmRz LA0KDQpQaG9lYmUNCg0K --------------fNf0i7ksF6iR3RXpy3OKuavz Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable

Dear Xiaohongshu team,=

my name is Phoebe and = I am a security researcher. For the past week I have been looking into the RedNote app and discovered severe issues in how the app interacts with the server API.

Technical details
=

Part of the network communication in the RedNote app (com.xingin.xhs) is unencrypted allowing adversaries to listen to the network and capture information about the user. This information includes what actions the user performs on your service (following accounts, liking posts, sending direct messages, etc.), but also information about the device the user is logging into the app on. All of this happens in the libxhslonglink.so shared library, where it creates a connection to one of the server IPs over port 5333 and sends packets containing a 12 byte header and a protobuf-encoded payload.

Some of the payloads d= o not leak too much information, but even just in the first couple of packets a SessionAuth proto message is sent and an AuthResp message is returned by the server. If an adversary, who we will call Eve, captures the SessionAuth of a user Alice, Eve can then save Alice's authentication information and at a later point in time authenticate as Alice in the API and perform other API actions through Alice's account. Essentially giving Eve complete control over Alice's account.

In some cases the SessionAuth will have a cipherType field set to 1, causing chat proto messages to be encrypted using AES128-ECB, but the key used for the encryption is also sent in plaintext in the AuthResp, thus allowing Eve to capture the key and decrypt all such packets as well.

As an additional issue= , the only information necessary to get authenticated with the server is a uid, an sid (token) and device information. Considering the uid is public information and the sid looks to be a nanosecond timestamp of account creation with some extra digits, this leaves about 6 digits (assuming the nanosecond precision is difficult to find) of security and device information keeping an account secure, which in itself is concerning and should be hardened.

Solutions

=

The app is capable of using TLS for communicating with the CDNs, so I would suggest migrating the control API to using TLS. Using a proprietary protocol usually sounds like a nice idea, but ultimately fails in practice, so I cannot stress enough how important it is to migrate to protocols that have been scrutinized in the past.

Considering the severity of the vulnerability it would be responsible to introduce a breaking change and force users to update instead of gradually migrating the APIs, since a transition phase would allow adversaries to collect as much information about your users as they can while the migration happens.

As for the issue with only needing a timestamp-formed sid and device information to login to an account, it is necessary that you improve the security of accounts and introduce e.g. a password scheme using hashed password strings, or other similar schemes that use information only known by the account holder and that cannot be guessed based on observable information.

Publication

The vulnerabilities I am bringing to your attention in this email will be publicized by the end of next week (the 23rd of February), even if not yet fixed. Although, I do understand updating code takes time and effort, so if you wish for me to delay bringing this issue to the public, feel free to reach out and we can discuss specifics.<= br>

In the end, my main priority is the security of your users, so I am open to any questions your team may have.


Kindest regards,

Phoebe

--------------fNf0i7ksF6iR3RXpy3OKuavz-- --------------m4C2lQ9CEb1Ql6Roklxoxecl Content-Type: application/pgp-keys; name="OpenPGP_0x9B3023BD4A39243B.asc" Content-Disposition: attachment; filename="OpenPGP_0x9B3023BD4A39243B.asc" Content-Description: OpenPGP public key Content-Transfer-Encoding: quoted-printable -----BEGIN PGP PUBLIC KEY BLOCK----- xjMEZxO/yBYJKwYBBAHaRw8BAQdAlagvf+uRL4Ug5npHaABJElUWLw5OxRF9r8Vm qCBus8jNJVBob2ViZSBEdXNpbCA8cGhvZWJlQGZsb3dlcmZpZWxkLmRldj7CkwQT FgoAOxYhBDxqjXxo2Rs9dKIdc5swI71KOSQ7BQJnE7/IAhsDBQsJCAcCAiICBhUK CQgLAgQWAgMBAh4HAheAAAoJEJswI71KOSQ7e6UBAMNPyq/fKCU6BC3KHcwN6ONZ UKbdbtNkoOpQdDiFHZPAAP4/t6xhnBxC35aCdwW9lgrS3NBsbKPK4jjjwq8Bdc5i DcKZBBMWCgBBAhsDBQsJCAcCAiICBhUKCQgLAgQWAgMBAh4HAheAFiEEPGqNfGjZ Gz10oh1zmzAjvUo5JDsFAmcYOoAFCQWoFTgACgkQmzAjvUo5JDuo5gD+Na0s6aqw IDR6qOkfbSfh3/liL9pvgALIDXcdSxiOlu0A+wdz4AAkZimjyQlaZ1VYcF6C9qB3 9A8alJ43kg8uUW4HzjgEZxO/yBIKKwYBBAGXVQEFAQEHQEzuHC8UPP86cSoa2V6G fCoNJsauYEEAyUKdCiKUJWcxAwEIB8J4BBgWCgAgFiEEPGqNfGjZGz10oh1zmzAj vUo5JDsFAmcTv8gCGwwACgkQmzAjvUo5JDt3IQD/XU5qzaYJrPTwjoK+oNzHYSN5 w+2pXJOqe+5czc1A+yUA/jbF2HpFzHqXubCK9aadEB+DjJ/nHSH+tQhcSS36ue0P =3DsCtm -----END PGP PUBLIC KEY BLOCK----- --------------m4C2lQ9CEb1Ql6Roklxoxecl-- --------------FDXySm3eSRGq0eQWzxiUgbuc-- --------------81Crbut4NxK0WJp0kz00yQp0 Content-Type: application/pgp-signature; name="OpenPGP_signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="OpenPGP_signature.asc" -----BEGIN PGP SIGNATURE----- wnsEABYIACMWIQQ8ao18aNkbPXSiHXObMCO9SjkkOwUCZ7BvhQUDAAAAAAAKCRCbMCO9SjkkO/6e AP4gMoazg/Yi7D+3fcUJs6MGQLL9lr7ThMSWhZeV69XzqQEAkH3Pa1Do+bGYcr4a4chzR1gfCh22 bs+Fv1JiJQz7vAI= =K9lB -----END PGP SIGNATURE----- --------------81Crbut4NxK0WJp0kz00yQp0--