hyper's HTTP header parser accepted, according to RFC 7230, illegal contents inside Content-Length headers. Due to this, upstream HTTP proxies that ignore the header may still forward them along if it chooses to ignore the error.

To be vulnerable, hyper must be used as an HTTP/1 server and using an HTTP proxy upstream that ignores the header's contents but still forwards it. Due to all the factors that must line up, an attack exploiting this vulnerability is unlikely.

When decoding chunk sizes that are too large, hyper's code would encounter an integer overflow. Depending on the situation, this could lead to data loss from an incorrect total size, or in rarer cases, a request smuggling attack.

To be vulnerable, you must be using hyper for any HTTP/1 purpose, including as a client or server, and consumers must send requests or responses that specify a chunk size greater than 18 exabytes. For a possible request smuggling attack to be possible, any upstream proxies must accept a chunk size greater than 64 bits.

The following Rust program demonstrates some strangeness in AES encryption - if you have an immutable key slice and then operate on that slice, you get different encryption output than if you operate on a copy of that key.

For these functions, we expect that extending a 16 byte key to a 32 byte key by repeating it gives the same encrypted data, because the underlying rust-crypto functions repeat key data up to the necessary key size for the cipher.

use crypto::{
    aes, blockmodes, buffer,
    buffer::{BufferResult, ReadBuffer, WriteBuffer},
    symmetriccipher,
};

fn encrypt(
    key: &[u8],
    iv: &[u8],
    data: &str,
) -> Result<String, symmetriccipher::SymmetricCipherError> {
    let mut encryptor =
        aes::cbc_encryptor(aes::KeySize::KeySize256, key, iv, blockmodes::PkcsPadding);

    let mut encrypted_data = Vec::<u8>::new();
    let mut read_buffer = buffer::RefReadBuffer::new(data.as_bytes());
    let mut buffer = [0; 4096];
    let mut write_buffer = buffer::RefWriteBuffer::new(&mut buffer);

    loop {
        let result = encryptor.encrypt(&mut read_buffer, &mut write_buffer, true)?;

        encrypted_data.extend(
            write_buffer
                .take_read_buffer()
                .take_remaining()
                .iter()
                .copied(),
        );

        match result {
            BufferResult::BufferUnderflow => break,
            BufferResult::BufferOverflow => {}
        }
    }

    Ok(hex::encode(encrypted_data))
}

fn working() {
    let data = "data";
    let iv = [
        0xF0, 0xF1, 0xF2, 0xF3, 0xF4, 0xF5, 0xF6, 0xF7, 0xF8, 0xF9, 0xFA, 0xFB, 0xFC, 0xFD, 0xFE,
        0xFF,
    ];
    let key = [
        0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0A, 0x0B, 0x0C, 0x0D, 0x0E,
        0x0F,
    ];
    // The copy here makes the code work.
    let key_copy = key;
    let key2: Vec<u8> = key_copy.iter().cycle().take(32).copied().collect();
    println!("key1:{} key2: {}", hex::encode(&key), hex::encode(&key2));

    let x1 = encrypt(&key, &iv, data).unwrap();
    println!("X1: {}", x1);

    let x2 = encrypt(&key2, &iv, data).unwrap();
    println!("X2: {}", x2);

    assert_eq!(x1, x2);
}

fn broken() {
    let data = "data";
    let iv = [
        0xF0, 0xF1, 0xF2, 0xF3, 0xF4, 0xF5, 0xF6, 0xF7, 0xF8, 0xF9, 0xFA, 0xFB, 0xFC, 0xFD, 0xFE,
        0xFF,
    ];
    let key = [
        0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0A, 0x0B, 0x0C, 0x0D, 0x0E,
        0x0F,
    ];
    // This operation shouldn't affect the contents of key at all.
    let key2: Vec<u8> = key.iter().cycle().take(32).copied().collect();
    println!("key1:{} key2: {}", hex::encode(&key), hex::encode(&key2));

    let x1 = encrypt(&key, &iv, data).unwrap();
    println!("X1: {}", x1);

    let x2 = encrypt(&key2, &iv, data).unwrap();
    println!("X2: {}", x2);

    assert_eq!(x1, x2);
}

fn main() {
    working();
    broken();
}

The output from this program:

     Running `target/host/debug/rust-crypto-test`
key1:000102030405060708090a0b0c0d0e0f key2: 000102030405060708090a0b0c0d0e0f000102030405060708090a0b0c0d0e0f
X1: 90462bbe32965c8e7ea0addbbed4cddb
X2: 90462bbe32965c8e7ea0addbbed4cddb
key1:000102030405060708090a0b0c0d0e0f key2: 000102030405060708090a0b0c0d0e0f000102030405060708090a0b0c0d0e0f
X1: 26e847e5e7df1947bf82a650548a7d5b
X2: 90462bbe32965c8e7ea0addbbed4cddb
thread 'main' panicked at 'assertion failed: `(left == right)`
  left: `"26e847e5e7df1947bf82a650548a7d5b"`,
 right: `"90462bbe32965c8e7ea0addbbed4cddb"`', src/main.rs:83:5

Notably, the X1 key in the broken() test changes every time after rerunning the program.

When this crate is given a pathological certificate chain to validate, it will spend CPU time exponential with the number of candidate certificates at each step of path building.

Both TLS clients and TLS servers that accept client certificate are affected.

This was previously reported in https://github.com/briansmith/webpki/issues/69 and re-reported recently by Luke Malinowski.

webpki 0.22.1 included a partial fix and webpki 0.22.2 added further fixes.

If a close_notify alert is received during a handshake, complete_io does not terminate.

Callers which do not call complete_io are not affected.

rustls-tokio and rustls-ffi do not call complete_io and are not affected.

rustls::Stream and rustls::StreamOwned types use complete_io and are affected.