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.

A security regression (CVE-2006-5051) was discovered in OpenSSH's server (sshd). There is a race condition which can lead sshd to handle some signals in an unsafe manner. An unauthenticated, remote attacker may be able to trigger it by failing to authenticate within a set time period.

A fundamental design flaw within the RADIUS protocol has been proven to be exploitable, compromising the integrity in the RADIUS Access-Request process. The attack allows a malicious user to modify packets in a way that would be indistinguishable to a RADIUS client or server. To be successful, the attacker must have the ability to inject themselves between the client and server.

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A heap-based buffer overflow vulnerability [CWE-122] in FortiOS, FortiManager, FortiAnalyzer, FortiManager Cloud, FortiAnalyzer Cloud, FortiProxy fgfmd daemon may allow an authenticated attacker to execute arbitrary code or commands via specifically crafted requests.

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An Improper Neutralization of Special Elements used in an SQL Command ('SQL Injection') vulnerability [CWE-89] in FortiAnalyzer, FortiManager, FortiManager Cloud and FortiAnalyzer Cloud may allow a low privileged user to execute arbitrary commands via crafted requests.

A missing authentication for critical function vulnerability in Fortinet FortiManager 7.4.0 through 7.4.2, FortiManager 7.2.0 through 7.2.4, FortiManager 7.0.0 through 7.0.11, FortiManager 6.4.0 through 6.4.14, FortiOS 7.4.0 through 7.4.3, FortiOS 7.2.0 through 7.2.7, FortiOS 7.0.0 through 7.0.14, FortiOS 6.4 all versions, FortiOS 6.2 all versions, FortiOS 6.0 all versions, FortiPAM 1.2 all versions, FortiPAM 1.1 all versions, FortiPAM 1.0 all versions, FortiPortal 6.0.0 through 6.0.14, FortiPortal 5.3 all versions, FortiProxy 7.4.0 through 7.4.3, FortiProxy 7.2.0 through 7.2.9, FortiProxy 7.0.0 through 7.0.16, FortiProxy 2.0 all versions, FortiProxy 01.02 all versions, FortiProxy 1.2 all versions, FortiProxy 01.01 all versions, FortiProxy 1.1 all versions, FortiProxy 01.00 all versions, FortiSwitchManager 7.2.0 through 7.2.3, FortiSwitchManager 7.0.0 through 7.0.3 allows attacker to execute unauthorized code or commands via specially crafted packets.

A improper limitation of a pathname to a restricted directory ('path traversal') vulnerability in Fortinet FortiManager 7.6.0 through 7.6.1, FortiManager 7.4.1 through 7.4.3, FortiManager Cloud 7.4.1 through 7.4.3, FortiOS 7.6.0, FortiOS 7.4.0 through 7.4.4, FortiOS 7.2.0 through 7.2.9, FortiOS 7.0.0 through 7.0.15, FortiOS 6.4.0 through 6.4.15, FortiProxy 7.4.0 through 7.4.5, FortiProxy 7.2.0 through 7.2.11, FortiProxy 7.0.0 through 7.0.18, FortiProxy 2.0 all versions, FortiProxy 01.02 all versions, FortiProxy 1.2 all versions, FortiProxy 01.01 all versions, FortiProxy 1.1 all versions, FortiProxy 01.00 all versions may allow a remote authenticated attacker with access to the security fabric interface and port to write arbitrary files or a remote unauthenticated attacker to delete an arbitrary folder

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Researchers at Palo Alto Networks Unit 42 published an investigation into a sophisticated attack against a telecommunications provider.

The original intrusion occurred in September 2024, but the newly published analysis documents previously unreported malware.

Attackers initially exploited CVE-2024-47575 to compromise a FortiManager management appliance.

They obtained configuration files and sensitive information associated with more than 500 FortiGate firewalls.

The attackers subsequently deployed malware called PEERSTITCH.

Its unusual feature is that it operates inside the memory of legitimate firewall processes rather than maintaining a conventional malware file on disk.

The implant could manipulate VPN security checks while blending into normal network activity.

The researchers did not establish that all 500 managed firewalls were compromised.

This is an excellent example of why traditional antivirus scanning cannot detect every attack.

Malware operating in memory may leave fewer conventional file-based indicators.

An Improper Neutralization of Special Elements used in an SQL Command ('SQL Injection') vulnerability [CWE-89] in FortiAnalyzer, FortiManager, FortiManager Cloud and FortiAnalyzer Cloud may allow a low privileged user to execute arbitrary commands via crafted requests.

An Improper Neutralization of Special Elements used in an SQL Command ('SQL Injection') vulnerability [CWE-89] in FortiAnalyzer, FortiManager, FortiManager Cloud and FortiAnalyzer Cloud may allow a low privileged user to execute arbitrary commands via crafted requests.

A improper neutralization of special elements used in an os command ('os command injection') vulnerability in Fortinet FortiManager 8.0.0, FortiManager 7.6.0 through 7.6.6, FortiManager Cloud 7.6.2 through 7.6.6 may allow attacker to escalation of privilege via specially crafted packets

An improper neutralization of special elements used in an SQL command ('SQL injection') [CWE-89] in FortiAnalyzer, FortiAnalyzer Cloud, FortiManager and FortiManager Cloud may allow an authenticated privileged attacker to execute unauthorized code or commands via crafted requests.

An improper limitation of a pathname to a restricted directory ('path traversal') vulnerability in FortiAnalyzer, FortiAnalyzer Cloud, FortiManager and FortiManager Cloud may allow a privileged attacker to delete files from the underlying filesystem via crafted CLI requests.

A use of potentially Dangerous Function vulnerability [CWE-676] in FortiAnalyzer and FortiManager API may allow an authenticated attacker to cause a system hang via multiple specially crafted HTTP requests causing crashes. This happens if internal locks are aligned, which is out of control of the attacker.

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An improper neutralization of special elements used in an OS command ('OS Command Injection') vulnerability [CWE-78] in FortiManager fgfmd daemon may allow a remote attacker impersonating a fortimanager cluster node to execute unauthorized code or commands via specially crafted packets. Impersonation of a Fortimanager cluster node requires possessing the node's certificate and private key.

An Improper Neutralization of Special Elements used in an SQL Command ('SQL Injection') vulnerability [CWE-89] in FortiAnalyzer, FortiManager, FortiManager Cloud and FortiAnalyzer Cloud may allow a low privileged user to execute arbitrary commands via crafted requests.

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An improper access control vulnerability [CWE-284] in FortiManager may allow an administrator to bypass the approval process for workflow sessions via crafted HTTP or HTTPs requests.

Apache HTTP Server: modhttp2 denial of service

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CVE-2026-49975Memory Allocation with Excessive Size Value vulnerability in Apache HTTP Server's modhttp leads to denial of service via malicious HTTP requests. This issue affects Apache HTTP Server: from 2.4.17 through 2.4.67.

A incorrect privilege assignment vulnerability in Fortinet FortiAnalyzer 7.4.0 through 7.4.3, FortiAnalyzer 7.2.0 through 7.2.5, FortiAnalyzer 7.0 all versions, FortiAnalyzer 6.4 all versions, FortiAnalyzer Cloud 7.4.1 through 7.4.2, FortiAnalyzer Cloud 7.2.1 through 7.2.6, FortiAnalyzer Cloud 7.0 all versions, FortiAnalyzer Cloud 6.4 all versions, FortiManager 7.4.0 through 7.4.3, FortiManager 7.2.0 through 7.2.5, FortiManager 7.0 all versions, FortiManager 6.4 all versions allows attacker to escalate privilege via specific shell commands

A improper limitation of a pathname to a restricted directory ('path traversal') vulnerability in Fortinet FortiRecorder 7.2.0 through 7.2.1, FortiRecorder 7.0.0 through 7.0.4, FortiVoice 7.0.0 through 7.0.4, FortiVoice 6.4.0 through 6.4.9, FortiVoice 6.0 all versions, FortiWeb 7.6.0, FortiWeb 7.4.0 through 7.4.4, FortiWeb 7.2 all versions, FortiWeb 7.0 all versions, FortiWeb 6.4 all versions allows attacker to escalate privilege via specially crafted packets.

A stack-based buffer overflow vulnerability in Fortinet FortiAnalyzer 7.4.0 through 7.4.3, FortiAnalyzer 7.2.0 through 7.2.5, FortiAnalyzer 7.0.0 through 7.0.12, FortiAnalyzer 6.4.0 through 6.4.14, FortiAnalyzer Cloud 7.4.1 through 7.4.3, FortiAnalyzer Cloud 7.2.1 through 7.2.5, FortiAnalyzer Cloud 7.0.1 through 7.0.11, FortiAnalyzer Cloud 6.4 all versions, FortiManager 7.4.0 through 7.4.3, FortiManager 7.2.0 through 7.2.5, FortiManager 7.0.0 through 7.0.12, FortiManager 6.4.0 through 6.4.14, FortiManager Cloud 7.4.1 through 7.4.3, FortiManager Cloud 7.2.1 through 7.2.5, FortiManager Cloud 7.0.1 through 7.0.11, FortiManager Cloud 6.4 all versions allows attacker to execute unauthorized code or commands via specially crafted packets.