wolfSSH server accepts server-to-client DH group exchange messages from an unauthenticated client, causing pre-authentication primality-test CPU exhaustion and key exchange role confusion
Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).
| Vendor | Product | Default status | Versions | ||||||
|---|---|---|---|---|---|---|---|---|---|
| wolfSSL Inc. | wolfSSH | unaffected |
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No data.
| Vendor | Product | Versions | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Wolfssl | Wolfssh |
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Vendor Workaround
Build wolfSSH with WOLFSSH_NO_DH_GEX_SHA256 defined so that diffie-hellman-group-exchange-sha256 is neither offered nor accepted, which removes the message 31 dispatch path entirely. Where group exchange must stay available, lowering WOLFSSH_DEFAULT_GEXDH_MAX reduces the size of the value a peer can submit for primality testing and so the cost of a single packet, but it does not stop a server from accepting the message.
No CVSS v3.0
No CVSS v2
This CVE is not in the KEV list.
Exploit prediction score: < 1% (0.483% probability within 30 days)
| Type | Values Removed | Values Added |
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| First Time appeared |
Wolfssh
Wolfssh wolfssh |
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| CPEs | cpe:2.3:a:wolfssh:wolfssh:*:*:*:*:*:*:*:* | |
| Vendors & Products |
Wolfssh
Wolfssh wolfssh |
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| Metrics |
cvssV3_1
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| Type | Values Removed | Values Added |
|---|---|---|
| Metrics |
ssvc
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| Type | Values Removed | Values Added |
|---|---|---|
| First Time appeared |
Wolfssl
Wolfssl wolfssh |
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| Vendors & Products |
Wolfssl
Wolfssl wolfssh |
| Type | Values Removed | Values Added |
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| Description | src/internal.c in wolfSSL wolfSSH through 1.5.0 admits the server-to-client Diffie-Hellman group exchange messages SSH_MSG_KEX_DH_GEX_GROUP (31) and SSH_MSG_KEX_DH_GEX_REPLY (33) when a server receives them from an unauthenticated client. IsMessageAllowedServer() applies no direction check to the key exchange message range: when the peer is keying and no particular message is expected, which is the state a server is in for the whole window after it processes the client's KEXINIT because nothing sets handshake->expectMsgId there, the function falls out of its expectation branch without a verdict and reaches a numeric bound that admits every message id from 30 through 34. A client that negotiates diffie-hellman-group-exchange-sha256 and then sends message 31 makes the server run the client-side handler DoKexDhGexGroup(), which validates the attacker-supplied group with two 8-round Miller-Rabin primality tests, one on p and one on (p-1)/2, on a value of up to 8192 bits. The handler then returns success: the server stores the attacker's prime and generator, generates a Diffie-Hellman key pair in the attacker's group, and sends the client-role message SSH_MSG_KEX_DH_GEX_INIT (32) back to the attacker. Published RFC 3526 safe primes are the worst-case input and cost the attacker nothing to obtain. The primality validation was added in 1.5.0; versions from 1.2.0 through 1.4.22 admit the same message and enter the same client-role path without the primality cost. Message 33 is admitted as well, but on a server it is rejected before any cryptography because no public key check callback is registered, so it carries no comparable cost. Builds that define WOLFSSH_NO_DH_GEX_SHA256, which is implied by WOLFSSH_NO_DH or NO_SHA256, are unaffected. | |
| Title | wolfSSH server accepts server-to-client DH group exchange messages from an unauthenticated client, causing pre-authentication primality-test CPU exhaustion and key exchange role confusion | |
| Weaknesses | CWE-372 CWE-400 CWE-405 |
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| References |
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| Metrics |
cvssV4_0
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