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Warpgate EUVDEUVD-2026-84064

| CVE-2026-91166 MEDIUM
Improper Validation of Certificate with Host Mismatch (CWE-297)
2026-09-21 GitHub_M
5.7
CVSS 3.1 · Vendor: GitHub_M
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Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata – not a confirmed exploit chain

  1. Access
    Compromise or operate SSH jump host
  2. Delivery
    Victim browser-SSH connects to jump-routed target
  3. Exploit
    Warpgate stores jump key under target address
  4. Execution
    Present jump key at target via MITM
  5. Persist
    Accepted as target, intercept session
  6. Impact
    Capture traffic and issued certificate

Vulnerability Assessment

Weakness
CWE
OWASP Top 10:2025
A07:2025 - Authentication Failures
ASVS 5.0
V12 - Secure Communication Certificate host validation
Exploitation Conditions

Exploitation requires a specific chain of conditions, all of which limit real-world risk: (1) the victim must use Warpgate's browser/web SSH path (warpgate-web-ssh), not the native SSH proxy, which tracks each hop separately and is unaffected; (2) the accessed target must be reached through an SSH jump/proxy host so that a jump-host key is presented during connection; (3) the host-key verification mode must be Prompt or AutoAccept (so the jump key is stored under the target address - in Prompt mode a user must actively accept the key, matching UI:R); (4) the attacker must control the jump host or otherwise possess its private key in order to complete the SSH handshake when re-presenting that key; and (5) the attacker must hold a man-in-the-middle position at the target address. Impact is greatest when certificate authentication is used, since a new certificate is issued to the impersonating machine. Only versions 0.25.0 through before 0.27.6 are affected; upgrade to 0.27.6 removes the vulnerable web-SSH trust logic.

Impact

This is a genuine but high-barrier trust-confusion flaw, not a mass-exploitation priority. The vendor CVSS 3.1 vector (AV:N/AC:H/PR:H/UI:R/S:U/C:H/I:H/A:N, 5.7 Medium) already encodes multiple limiting gates: high attack complexity, high privileges, and required user interaction. No EPSS score, no CISA KEV listing, and no public POC are present in the intelligence - consistent with a subtle host-key-handling bug in a niche open-source bastion rather than a widely targeted vulnerability. The real risk is bounded by the exploitation preconditions rather than the network attack vector: the attacker must effectively control (hold the private key of) the SSH jump/proxy host, hold a network man-in-the-middle position at the target address, and rely on a target configured with a jump host in Prompt or AutoAccept host-key mode. One caveat on the metadata: the sole impact-oriented tag is 'Information Disclosure', which captures only the confidentiality (traffic interception) facet - the underlying weakness (CWE-297, host key/certificate host mismatch) is a spoofing/MITM issue that also has integrity impact (I:H, malicious acceptance as the target and issuance of a new certificate under cert auth). PR:H is defensible as a proxy for 'must control the jump host' but is debatable in strict CVSS terms because the attacker holds no privileges on the Warpgate component itself. Treat as a patch-in-normal-cycle item, prioritized higher only for deployments using browser SSH with jump hosts and certificate authentication.

Exploit ScenarioDerived

An operator uses Warpgate's browser (web) SSH to reach a target that is reached via an SSH jump host, in Prompt or AutoAccept host-key mode; Warpgate incorrectly stores the jump host's key under the target's address. An attacker who controls the jump host and can intercept traffic to the target later presents that same key at the target address, is accepted as the target, and intercepts the user's session - obtaining a freshly issued certificate when certificate authentication is in use. No public exploit code was identified at the time of analysis, and the high complexity plus required jump-host control make this an opportunistic-to-targeted scenario rather than a turnkey attack.

This Month Plan within 30 days. Why: MEDIUM severity (CVSS 4.0-6.9).
Patch available 0.2% exploitation probability (EPSS)

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AnalysisAIv1 – Sep 21, 2026

Host-key trust confusion in Warpgate's browser SSH client (warpgate-web-ssh) lets a malicious or compromised SSH jump host have its host key stored against the final target's address, so a machine later presenting that key at the target address is accepted as the intended destination - permitting interception of user traffic and, when certificate authentication is used, issuance of a fresh certificate to the impersonating host. Affected are Warpgate 0.25.0 through 0.27.5 on the Web SSH path only; the native SSH proxy tracks each hop separately and is unaffected. Exploitation requires a high-barrier chain (Web SSH session by an authenticated user per PR:H, a target reached through a jump/proxy hop, Prompt or AutoAccept host-key mode with UI:R in Prompt mode, attacker possession of the jump host's private key, and a man-in-the-middle position at the target), and no public exploit code has been identified at time of analysis, with the issue not appearing in CISA KEV.

RemediationAI

Vendor-released patch: upgrade to Warpgate 0.27.6 (https://github.com/warp-tech/warpgate/releases/tag/v0.27.6), the fix for GHSA-w9jj-vpw3-5r8f delivered by commit fb66ff74f979c22054f4d348cc0d9065cc67e5d3, which makes the Web SSH path record host keys against the hop that actually presented them; versions 0.25.0 through 0.27.5 require this upgrade. Until patching, avoid using the browser/Web SSH path to reach targets through SSH jump hosts and prefer the native SSH proxy path, which is unaffected by this flaw. Where Web SSH through jump hosts must stay in use, treat every jump host as trust-relevant and ensure it is one you control and monitor, since possession of a jump host's private key is a prerequisite for the attack; note that switching host-key verification to Ignore prevents the bogus entry from being stored but also disables host-key verification altogether, so it is a weakened configuration rather than a fix. After upgrading, review known_hosts entries created while Web SSH sessions traversed jump hosts, and rotate or reissue SSH certificates (and host keys) for any target that may have been impersonated, since certificate authentication is where the impact is most severe.

Affected VersionsENISA

warpgate 0.25.0, < 0.27.6

Affected Packages

euvd warpgate_0_25_0 fix: 0.27.6

Source: OSV (Open Source Vulnerabilities)

Affects your stack

Affects 1 package in euvd

Checking this CVE against your own stacks and servers is part of the Basic plan and up.

Technical ContextAI · show details

Warpgate is a Rust-based Linux bastion host that proxies SSH, HTTPS and MySQL; its browser front end (warpgate-web-ssh) drives the shared SSH client implemented in warpgate-protocol-ssh. The root cause is CWE-297 (improper validation of certificate with host mismatch): the RCEvent::HostKeyUnknown event carried only the presented public key and a reply channel, with no identity for the hop that presented the key. In warpgate-web-ssh/src/manager.rs the handler therefore called KnownHosts::trust using ssh_options.host and ssh_options.port - the address of the final target - instead of the address of the hop (the jump host) that actually presented the unknown key. In Prompt and AutoAccept verification modes that mismatch persisted a jump-host key in known_hosts under the target's entry, so a later connection to that target would accept whichever server presented that jump-host key, defeating host-key authentication for the target. The native SSH path in warpgate-protocol-ssh/src/server/session.rs keeps per-hop context and was not affected. The fix (commit fb66ff74f979c22054f4d348cc0d9065cc67e5d3, released as v0.27.6) extends the RCEvent::HostKeyUnknown variant with host and port fields, propagates the presenting hop's identity into the trust decision, and removes the duplicated trust call in warpgate-web-ssh/src/api.rs.

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Severity by source

Vendor (GitHub_M) PRIMARY 5.7 MEDIUM
AV:N/AC:H/PR:H/UI:R/S:U/C:H/I:H/A:N
vuln.today AI 5.7 MEDIUM

AC:H and UI:R for the required jump-host config, host-key mode, MITM position and user acceptance; PR:H models mandatory control of the jump host; C:H/I:H for traffic interception and impersonation, A:N.

3.1 AV:N/AC:H/PR:H/UI:R/S:U/C:H/I:H/A:N
4.0 AV:N/AC:H/AT:P/PR:H/UI:A/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N

Primary rating from Vendor (GitHub_M).

CVSS VectorVendor: GitHub_M

Attack Vector
Network
Attack Complexity
High
Privileges Required
High
User Interaction
Required
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
None

Lifecycle Timeline

2
Patch available
Sep 21, 2026 - 20:02 EUVD
CVE Published
Sep 21, 2026 - 18:53 cve.org
MEDIUM 5.7

DescriptionCVE.org

Warpgate is an open source SSH, HTTPS and MySQL bastion host for Linux. From 0.25.0 until 0.27.6, the browser SSH path in warpgate-web-ssh/src/manager.rs handles RCEvent::HostKeyUnknown without the presenting hop identity and instead passes ssh_options.host and ssh_options.port for the final target to KnownHosts::trust. In Prompt and AutoAccept modes, a jump host key can therefore be stored for the target address. A machine later presenting the jump host key at the target address can be accepted as the target, allowing interception of user traffic and a newly issued certificate when certificate authentication is used. The native SSH path is unaffected because it tracks each hop separately. This issue is fixed in version 0.27.6.

Threat Intelligence Overview

EPSS Score
0.2%
Top 93% exploitable
Prevalence
Low
niche self-hosted open-source SSH/HTTPS/MySQL bastion, limited enterprise footprint
Data Quality
5 sources
Confidence: Medium

How this decision was reached

The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.

SignalValue
Severity MEDIUM
CISA KEV No
Public POC No
EPSS 0.2%
Patch available Yes
Active threat No
Deciding rule
MEDIUM severity (CVSS 4.0-6.9)
What every action level means
Emergency Immediate action required. Criteria: CRITICAL + in CISA KEV (actively exploited) without patch, OR CRITICAL + EPSS > 30% without patch, OR CRITICAL + active threat signals without patch.
Act Now Prioritize within 24-48h. Criteria: in KEV with patch available, OR CRITICAL + public POC, OR HIGH + EPSS > 10%, OR CRITICAL + active threat, OR any CRITICAL severity.
This Week Schedule remediation this week. Criteria: HIGH severity (CVSS 7.0-8.9). Patch within normal change window.
This Month Plan within 30 days. Criteria: MEDIUM severity (CVSS 4.0-6.9), lower exploitation probability. Include in regular patch cycle.
Monitor Track and reassess. Criteria: LOW severity (CVSS 0.1-3.9), minimal exploitation risk. No immediate action needed.

SSVC AssessmentENISA

SSVC Decision· derived
Scheduled
Exploitation· derived
None
System Exposure· derived
Open
Automatable· derived
No
Human Impact· derived
Medium

Priority Score

28
Low Medium High Critical
KEV: 0
EPSS: 0
CVSS: +28
PoC: 0
Weaponized: 0
Threat intel: 0
Gov advisory: 0

Attack Technique

Information disclosure occurs when an application unintentionally exposes sensitive data that aids attackers in reconnaissance or directly compromises security.

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