EUVD-2026-23295Severity by source
AV:N/AC:H/PR:L/UI:R/S:U/C:H/I:N/A:N
AC:H reflects dual prerequisites (vault file write plus network interception); PR:L for write access to vault config; C:H for OAuth token theft enabling full Hub API impersonation.
Primary rating from GitHub Advisory.
CVSS VectorGitHub Advisory
Lifecycle Timeline
6DescriptionGitHub Advisory
Cryptomator is an open-source client-side encryption application for cloud storage. Version 1.19.1 contains a logic flaw in CheckHostTrustController.getAuthority() that allows an attacker to bypass the security fix for CVE-2026-32303. The method hardcodes the URI scheme based on port number, causing HTTPS URLs with port 80 to produce the same authority string as HTTP URLs, which defeats both the consistency check and the HTTP block validation. An attacker with write access to a cloud-synced vault.cryptomator file can craft a Hub configuration where apiBaseUrl and authEndpoint use HTTPS with port 80 to pass auto-trust validation, while tokenEndpoint uses plaintext HTTP. The vault is auto-trusted without user prompt, and a network-positioned attacker can intercept the OAuth token exchange to access the Cryptomator Hub API as the victim. This issue has been fixed in version 1.19.2.
AnalysisAI
OAuth token interception in Cryptomator 1.19.1 is enabled by a logic flaw in CheckHostTrustController.getAuthority() that re-opens the attack surface addressed by CVE-2026-32303. An attacker with write access to a cloud-synced vault.cryptomator file can craft a Hub configuration mixing HTTPS-on-port-80 and plaintext HTTP endpoints, causing the application to auto-trust the vault without prompting the user while routing the OAuth tokenEndpoint over unencrypted HTTP. A network-positioned attacker who intercepts that exchange gains the victim's OAuth token and can authenticate to the Cryptomator Hub API on their behalf. No public exploit identified at time of analysis (SSVC lists poc), and EPSS sits at the 1st percentile, indicating low widespread exploitation probability. Vendor-released patch available in version 1.19.2.
Technical ContextAI
Cryptomator Hub integration uses an OAuth 2.0 flow to authenticate users against a self-hosted or managed Hub instance. The client validates Hub trustworthiness through CheckHostTrustController, which in version 1.19.1 derives the URI scheme solely from port number inside getAuthority(): port 80 is always resolved as HTTP regardless of whether the supplied URL specifies HTTPS. This produces identical authority strings for https://hub.example.com:80/api and http://hub.example.com/api, defeating both the consistency check (which compares authority strings for apiBaseUrl and authEndpoint) and the HTTP-blocking guard. The root cause is CWE-305 (Authentication Bypass by Primary Weakness): a flawed normalization step causes the security decision to operate on corrupted data, rendering the host-trust validation meaningless. CPE cpe:2.3:a:cryptomator:cryptomator:*:*:*:*:*:*:*:* scopes this to the Cryptomator desktop client at version 1.19.1 specifically. The PR diff confirms the fix added explicit enablement of Trust On First Use as a controlled flag rather than relying on the broken port-based scheme inference.
RemediationAI
Upgrade to Cryptomator 1.19.2, confirmed available at https://github.com/cryptomator/cryptomator/releases/tag/1.19.2, which resolves the getAuthority() scheme-derivation flaw. The upstream fix is documented in PR #4179 at https://github.com/cryptomator/cryptomator/pull/4179. If immediate upgrade is not feasible, restrict write access to vault.cryptomator files in cloud storage to only trusted principals - this prevents injection of a malicious Hub configuration and is the most effective compensating control, though it may disrupt legitimate vault-sharing workflows. Additionally, deploy network monitoring to alert on OAuth token requests from Cryptomator clients over plaintext HTTP, which would indicate active exploitation of this or similar HTTP-downgrade issues. Disabling Cryptomator Hub integration entirely removes the attack surface if Hub functionality is not required.
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External POC / Exploit Code
Leaving vuln.today