golang.org/x/crypto known bugs

The Go SSH library (golang.org/x/crypto/ssh) by default does not verify host keys, facilitating man-in-the-middle attacks if ClientConfig.HostKeyCallback is not set. Default behavior changed in commit e4e2799 to require explicitly registering a hostkey verification mechanism.

SSH servers which implement file transfer protocols are vulnerable to a denial of service attack from clients which complete the key exchange slowly, or not at all, causing pending content to be read into memory, but never transmitted.

The x/crypto/ssh package before 0.0.0-20211202192323-5770296d904e of golang.org/x/crypto allows an unauthenticated attacker to panic an SSH server. When using AES-GCM or ChaCha20Poly1305, consuming a malformed packet which contains an empty plaintext causes a panic.

golang.org/x/crypto before v0.0.0-20200220183623-bac4c82f6975 for Go allows a panic during signature verification in the golang.org/x/crypto/ssh package. A client can attack an SSH server that accepts public keys. Also, a server can attack any SSH client.

The Helm core maintainers have identified a high severity security vulnerability in Go's `crypto` package affecting all versions prior to Helm 2.16.8 and Helm 3.1.0. Thanks to @ravin9249 for identifying the vulnerability. ### Impact Go before 1.12.16 and 1.13.x before 1.13.7 (and the `crypto/cryptobyte` package before 0.0.0-20200124225646-8b5121be2f68 for Go) allows attacks on clients resulting in a panic via a malformed X.509 certificate. This may allow a remote attacker to cause a denial of service. ### Patches A patch to compile Helm against Go 1.14.4 has been provided for Helm 2 and is available in Helm 2.16.8. Helm 3.1.0 and newer are compiled against Go 1.13.7+. ### Workarounds No workaround is available. Users are urged to upgrade. ### References - https://nvd.nist.gov/vuln/detail/CVE-2020-7919 - https://github.com/helm/helm/pull/8288 ### For more information If you have any questions or comments about this advisory: * Open an issue in [the Helm repository](https://github.com/helm/helm/issues) * For security-specific issues, email us at <[email protected]>

The golang.org/x/crypto/ssh package before 0.0.0-20220314234659-1baeb1ce4c0b for Go allows an attacker to crash a server in certain circumstances involving AddHostKey.

A nil pointer dereference in the golang.org/x/crypto/ssh component through v0.0.0-20201203163018-be400aefbc4c for Go allows remote attackers to cause a denial of service against SSH servers. An attacker can craft an authentication request message for the `gssapi-with-mic` method which will cause NewServerConn to panic via a nil pointer dereference if ServerConfig.GSSAPIWithMICConfig is nil.

SSH Agent servers do not validate the size of messages when processing new identity requests, which may cause the program to panic if the message is malformed due to an out of bounds read.

SSH servers parsing GSSAPI authentication requests do not validate the number of mechanisms specified in the request, allowing an attacker to cause unbounded memory consumption.

SSH clients receiving SSH_AGENT_SUCCESS when expecting a typed response will panic and cause early termination of the client process.

SSH servers which implement file transfer protocols are vulnerable to a denial of service attack from clients which complete the key exchange slowly, or not at all, causing pending content to be read into memory, but never transmitted.

Applications and libraries which misuse connection.serverAuthenticate (via callback field ServerConfig.PublicKeyCallback) may be susceptible to an authorization bypass. The documentation for ServerConfig.PublicKeyCallback says that "A call to this function does not guarantee that the key offered is in fact used to authenticate." Specifically, the SSH protocol allows clients to inquire about whether a public key is acceptable before proving control of the corresponding private key. PublicKeyCallback may be called with multiple keys, and the order in which the keys were provided cannot be used to infer which key the client successfully authenticated with, if any. Some applications, which store the key(s) passed to PublicKeyCallback (or derived information) and make security relevant determinations based on it once the connection is established, may make incorrect assumptions. For example, an attacker may send public keys A and B, and then authenticate with A. PublicKeyCallback would be called only twice, first with A and then with B. A vulnerable application may then make authorization decisions based on key B for which the attacker does not actually control the private key. Since this API is widely misused, as a partial mitigation golang.org/x/[email protected] enforces the property that, when successfully authenticating via public key, the last key passed to ServerConfig.PublicKeyCallback will be the key used to authenticate the connection. PublicKeyCallback will now be called multiple times with the same key, if necessary. Note that the client may still not control the last key passed to PublicKeyCallback if the connection is then authenticated with a different method, such as PasswordCallback, KeyboardInteractiveCallback, or NoClientAuth. Users should be using the Extensions field of the Permissions return value from the various authentication callbacks to record data associated with the authentication attempt instead of referencing external state. Once the connection is established the state corresponding to the successful authentication attempt can be retrieved via the ServerConn.Permissions field. Note that some third-party libraries misuse the Permissions type by sharing it across authentication attempts; users of third-party libraries should refer to the relevant projects for guidance.

httpTokenCacheKey uses path.Base to extract the expected HTTP-01 token value to lookup in the DirCache implementation. On Windows, path.Base acts differently to filepath.Base, since Windows uses a different path separator (\ vs. /), allowing a user to provide a relative path, i.e. .well-known/acme-challenge/..\..\asd becomes ..\..\asd. The extracted path is then suffixed with +http-01, joined with the cache directory, and opened. Since the controlled path is suffixed with +http-01 before opening, the impact of this is significantly limited, since it only allows reading arbitrary files on the system if and only if they have this suffix.

A protocol weakness allows a MITM attacker to compromise the integrity of the secure channel before it is established, allowing the attacker to prevent transmission of a number of messages immediately after the secure channel is established without either side being aware. The impact of this attack is relatively limited, as it does not compromise confidentiality of the channel. Notably this attack would allow an attacker to prevent the transmission of the SSH2_MSG_EXT_INFO message, disabling a handful of newer security features. This protocol weakness was also fixed in OpenSSH 9.6.

The clearsign package accepts some malformed messages, making it possible for an attacker to trick a human user (but not a Go program) into thinking unverified text is part of the message. With fix, messages with malformed headers in the SIGNED MESSAGE section are rejected.

Unauthenticated clients can cause a panic in SSH servers. When using AES-GCM or ChaCha20Poly1305, consuming a malformed packet which contains an empty plaintext causes a panic.

On 32-bit architectures, a malformed input to crypto/x509 or the ASN.1 parsing functions of golang.org/x/crypto/cryptobyte can lead to a panic. The malformed certificate can be delivered via a crypto/tls connection to a client, or to a server that accepts client certificates. net/http clients can be made to crash by an HTTPS server, while net/http servers that accept client certificates will recover the panic and are unaffected.

XORKeyStream generates incorrect and insecure output for very large inputs. If more than 256 GiB of keystream is generated, or if the counter otherwise grows greater than 32 bits, the amd64 implementation will first generate incorrect output, and then cycle back to previously generated keystream. Repeated keystream bytes can lead to loss of confidentiality in encryption applications, or to predictability in CSPRNG applications. The issue might affect uses of golang.org/x/crypto/nacl with extremely large messages. Architectures other than amd64 and uses that generate less than 256 GiB of keystream for a single salsa20.XORKeyStream invocation are unaffected.

Attackers can cause a crash in SSH servers when the server has been configured by passing a Signer to ServerConfig.AddHostKey such that 1) the Signer passed to AddHostKey does not implement AlgorithmSigner, and 2) the Signer passed to AddHostKey returns a key of type “ssh-rsa” from its PublicKey method. Servers that only use Signer implementations provided by the ssh package are unaffected.

Clients can cause a panic in SSH servers. An attacker can craft an authentication request message for the “gssapi-with-mic” method which will cause NewServerConn to panic via a nil pointer dereference if ServerConfig.GSSAPIWithMICConfig is nil.

By default host key verification is disabled which allows for man-in-the-middle attacks against SSH clients if ClientConfig.HostKeyCallback is not set.

An attacker can craft an ssh-ed25519 or [email protected] public key, such that the library will panic when trying to verify a signature with it. If verifying signatures using user supplied public keys, this may be used as a denial of service vector.

A message-forgery issue was discovered in `crypto/openpgp/clearsign/clearsign.go` in supplementary Go cryptography libraries 2019-03-25. According to the OpenPGP Message Format specification in RFC 4880 chapter 7, a cleartext signed message can contain one or more optional "Hash" Armor Headers. The "Hash" Armor Header specifies the message digest algorithm(s) used for the signature. However, the Go clearsign package ignores the value of this header, which allows an attacker to spoof it. Consequently, an attacker can lead a victim to believe the signature was generated using a different message digest algorithm than what was actually used. Moreover, since the library skips Armor Header parsing in general, an attacker can not only embed arbitrary Armor Headers, but also prepend arbitrary text to cleartext messages without invalidating the signatures.

An issue was discovered in supplementary Go cryptography libraries, aka golang-googlecode-go-crypto, before 2019-03-20. A flaw was found in the amd64 implementation of golang.org/x/crypto/salsa20 and golang.org/x/crypto/salsa20/salsa. If more than 256 GiB of keystream is generated, or if the counter otherwise grows greater than 32 bits, the amd64 implementation will first generate incorrect output, and then cycle back to previously generated keystream. Repeated keystream bytes can lead to loss of confidentiality in encryption applications, or to predictability in CSPRNG applications. ### Specific Go Packages Affected golang.org/x/crypto/salsa20/salsa

SSH servers parsing GSSAPI authentication requests do not validate the number of mechanisms specified in the request, allowing an attacker to cause unbounded memory consumption.

SSH Agent servers do not validate the size of messages when processing new identity requests, which may cause the program to panic if the message is malformed due to an out of bounds read.

### Summary Terrapin is a prefix truncation attack targeting the SSH protocol. More precisely, Terrapin breaks the integrity of SSH's secure channel. By carefully adjusting the sequence numbers during the handshake, an attacker can remove an arbitrary amount of messages sent by the client or server at the beginning of the secure channel without the client or server noticing it. ### Mitigations To mitigate this protocol vulnerability, OpenSSH suggested a so-called "strict kex" which alters the SSH handshake to ensure a Man-in-the-Middle attacker cannot introduce unauthenticated messages as well as convey sequence number manipulation across handshakes. **Warning: To take effect, both the client and server must support this countermeasure.** As a stop-gap measure, peers may also (temporarily) disable the affected algorithms and use unaffected alternatives like AES-GCM instead until patches are available. ### Details The SSH specifications of ChaCha20-Poly1305 ([email protected]) and Encrypt-then-MAC (*[email protected] MACs) are vulnerable against an arbitrary prefix truncation attack (a.k.a. Terrapin attack). This allows for an extension negotiation downgrade by stripping the SSH_MSG_EXT_INFO sent after the first message after SSH_MSG_NEWKEYS, downgrading security, and disabling attack countermeasures in some versions of OpenSSH. When targeting Encrypt-then-MAC, this attack requires the use of a CBC cipher to be practically exploitable due to the internal workings of the cipher mode. Additionally, this novel attack technique can be used to exploit previously unexploitable implementation flaws in a Man-in-the-Middle scenario. The attack works by an attacker injecting an arbitrary number of SSH_MSG_IGNORE messages during the initial key exchange and consequently removing the same number of messages just after the initial key exchange has concluded. This is possible due to missing authentication of the excess SSH_MSG_IGNORE messages and the fact that the implicit sequence numbers used within the SSH protocol are only checked after the initial key exchange. In the case of ChaCha20-Poly1305, the attack is guaranteed to work on every connection as this cipher does not maintain an internal state other than the message's sequence number. In the case of Encrypt-Then-MAC, practical exploitation requires the use of a CBC cipher; while theoretical integrity is broken for all ciphers when using this mode, message processing will fail at the application layer for CTR and stream ciphers. For more details see [https://terrapin-attack.com](https://terrapin-attack.com). ### Impact This attack targets the specification of ChaCha20-Poly1305 ([email protected]) and Encrypt-then-MAC (*[email protected]), which are widely adopted by well-known SSH implementations and can be considered de-facto standard. These algorithms can be practically exploited; however, in the case of Encrypt-Then-MAC, we additionally require the use of a CBC cipher. As a consequence, this attack works against all well-behaving SSH implementations supporting either of those algorithms and can be used to downgrade (but not fully strip) connection security in case SSH extension negotiation (RFC8308) is supported. The attack may also enable attackers to exploit certain implementation flaws in a man-in-the-middle (MitM) scenario.

Applications and libraries which misuse the ServerConfig.PublicKeyCallback callback may be susceptible to an authorization bypass. The documentation for ServerConfig.PublicKeyCallback says that "A call to this function does not guarantee that the key offered is in fact used to authenticate." Specifically, the SSH protocol allows clients to inquire about whether a public key is acceptable before proving control of the corresponding private key. PublicKeyCallback may be called with multiple keys, and the order in which the keys were provided cannot be used to infer which key the client successfully authenticated with, if any. Some applications, which store the key(s) passed to PublicKeyCallback (or derived information) and make security relevant determinations based on it once the connection is established, may make incorrect assumptions. For example, an attacker may send public keys A and B, and then authenticate with A. PublicKeyCallback would be called only twice, first with A and then with B. A vulnerable application may then make authorization decisions based on key B for which the attacker does not actually control the private key. Since this API is widely misused, as a partial mitigation golang.org/x/[email protected] enforces the property that, when successfully authenticating via public key, the last key passed to ServerConfig.PublicKeyCallback will be the key used to authenticate the connection. PublicKeyCallback will now be called multiple times with the same key, if necessary. Note that the client may still not control the last key passed to PublicKeyCallback if the connection is then authenticated with a different method, such as PasswordCallback, KeyboardInteractiveCallback, or NoClientAuth. Users should be using the Extensions field of the Permissions return value from the various authentication callbacks to record data associated with the authentication attempt instead of referencing external state. Once the connection is established the state corresponding to the successful authentication attempt can be retrieved via the ServerConn.Permissions field. Note that some third-party libraries misuse the Permissions type by sharing it across authentication attempts; users of third-party libraries should refer to the relevant projects for guidance.