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 (chacha20-poly1305@openssh.com) and Encrypt-then-MAC (-etm@openssh.com MACs) are vulnerable against an arbitrary prefix truncation attack (a.k.a. Terrapin attack). This allows for an extension negotiation downgrade by stripping the SSHMSGEXTINFO sent after the first message after SSHMSGNEWKEYS, 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 SSHMSGIGNORE 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 SSHMSGIGNORE 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.
Impact
This attack targets the specification of ChaCha20-Poly1305 (chacha20-poly1305@openssh.com) and Encrypt-then-MAC (-etm@openssh.com), 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.
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A trusted URL can fool both users and automation into believing that the URL is safe when in fact it redirects to a malicious server. This can result in a victim inadvertently trusting the destination of the redirect, potentially leading to a successful phishing attack or other types of attacks.
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Duplicate Advisory This advisory has been withdrawn because it is a duplicate of GHSA-9vm7-v8wj-3fqw. This link is maintained to preserve external references.
Original Description A flaw was found in Keycloak. This issue may allow an attacker to steal authorization codes or tokens from clients using a wildcard in the JARM response mode "formpost.jwt" which could be used to bypass the security patch implemented to address CVE-2023-6134.
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It was found that Picketlink implementation replaces special strings for obtaining attribute values with system property values in SAML messages while parsing. An attacker can misuse this to determine values of system properties at the attacked system by formatting the SAML request ID field to the chosen system property name of his liking, obtaining the property value in "InResponseTo" field in the response.
Upstream bug (for Keycloak):
https://issues.jboss.org/browse/KEYCLOAK-4160
Duplicate Advisory This advisory has been withdrawn because it is a duplicate of GHSA-5cc8-pgp5-7mpm. This link is maintained to preserve external references.
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References:
https://issues.redhat.com/browse/KEYCLOAK-12638
Duplicate Advisory This advisory has been withdrawn because it is a duplicate of GHSA-gc7q-jgjv-vjr2. This link is maintained to preserve external references.
Original Description A vulnerability was found in Keycloak. This flaw allows attackers to bypass brute force protection by exploiting the timing of login attempts. By initiating multiple login requests simultaneously, attackers can exceed the configured limits for failed attempts before the system locks them out. This timing loophole enables attackers to make more guesses at passwords than intended, potentially compromising account security on affected systems.
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A flaw was found in Keycloak 7.0.1. A logged in user can do an account email enumeration attack.
ClassLoaderTheme and ClasspathThemeResourceProviderFactory allows reading any file available as a resource to the classloader. By sending requests for theme resources with a relative path from an external HTTP client, the client will receive the content of random files if available.
A POST based reflected Cross Site Scripting vulnerability on has been identified in Keycloak.
Keycloak implented HMAC verification using a comparison method that does not operate in constant time. This potentially leaves the application open to timing attacks.
https://issues.jboss.org/browse/KEYCLOAK-3667
A flaw was found in Keycloak before 13.0.0, where it is possible to force the server to call out an unverified URL using the OIDC parameter requesturi. This flaw allows an attacker to use this parameter to execute a Server-side request forgery (SSRF) attack.
A flaw was found in Keycloak before version 12.0.0, where it is possible to add unsafe schemes for the redirecturi parameter. This flaw allows an attacker to perform a Cross-site scripting attack.
A flaw was found in Keycloak's data filter, in version 10.0.1, where it allowed the processing of data URLs in some circumstances. This flaw allows an attacker to conduct cross-site scripting or further attacks.