Vulnerability · Published Sep 29, 2026 · Assigned by VulnCheck

CVE-2026-101878Bitwarden Server 2025.6.0 < 2025.6.0 Authentication Bypass via SSO Identifier Truncation

High 7.5

In plain English

A high-severity security flaw in bitwarden server from bitwarden. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 18% of all known vulnerabilities).

Severity (CVSS 3.1)7.5High

Exploit odds (30 days)0.3%top 82.4% of all CVEs

Exploited in the wildNo reportsCISA SSVC: poc

Attack toolingNoneno public tooling known

Official description

Bitwarden Server 2025.6.0 before 2026.5.0 declares the @ExternalId parameter of the User_ReadBySsoUserOrganizationIdExternalId stored procedure as NVARCHAR(50) while the column it queries stores NVARCHAR(300), silently truncating the SSO login identifier on SQL Server deployments and allowing a user whose identity-provider identifier begins with another organization member's full 50-character identifier to authenticate as that member and obtain a victim-scoped access token.

Affected products (as reported)

Vendor	Product	Versions
bitwarden	bitwarden server	2025.6.0 – before 2026.5.0

Weakness: CWE-303 · Vector: CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H

References

Researcher Blog technical-description, exploit
Release Notes release-notes
Pull Request issue-tracking
Patch Commit patch
https://www.vulncheck.com/advisories/bitwarden-server-authentication-bypass-via-sso-identifier-truncation third-party-advisory