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CVE-2026-102631— authd: Account takeover via username fallback in identity matching after IdP email reassignment

Quick assessment

Affected
Canonical authd
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

在 authd 0.7.1 版本之前， 函数（位于 ）中用于用户身份匹配的逻辑存在缺陷：该函数通过代理（broker）作用域内的提供者 ID 来解析 incoming 登录请求；当该提供者 ID 未关联到任何已知用户时，它会回退到使用用户名进行匹配；并且，对于非空且冲突的提供者 ID，它不会予以拒绝。 如果某个身份提供商（IdP）将曾经绑定到某一用户的电子邮件地址（authd 将其用作用户名）重新分配给一个新账户，那么该新账户在下次登录时，将继承原用户的本地 UID 和主目录。这会导致新用户可以访问和修改属于原用户

CVSS 5.9 · Medium

Affected Version Matrix 3

VendorProduct Version RangeStatus
Canonical authd 0.1< 0.7.1 affected
0.1< 0.7.1~ubuntu24.04.1 affected
0.1< 0.7.1~ubuntu26.04 affected
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I. Basic Information for CVE-2026-102631

Vulnerability Information
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Vulnerability Title
authd: Account takeover via username fallback in identity matching after IdP email reassignment
Source: CVE Program / CVE List V5
Vulnerability Description
In authd before 0.7.1, the user identity matching in UpdateUser (internal/users/manager.go) resolves an incoming login by the broker-scoped provider ID, but falls back to matching the username when the provider ID does not belong to any known user, and does not reject a conflicting non-empty provider ID. If an identity provider reassigns an email address, which authd uses as the username, to a new account, the new account inherits the previous user's local UID and home directory on its next login. This allows the new user to access and modify files belonging to the previous user, including credentials such as SSH keys and cloud API tokens, and silently rebinds the local account record to the new identity. As a mitigation, administrators should lock or delete the previous user's local authd account when the corresponding IdP account is removed.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:4.0/AV:L/AC:H/AT:P/PR:N/UI:N/VC:H/VI:L/VA:N/SC:N/SI:N/SA:N
Source: CVE Program / CVE List V5
Vulnerability Type
认证机制不恰当
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
Canonical authd 0.1 ~ 0.7.1 -

II. Public POCs for CVE-2026-102631

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III. Intelligence Information for CVE-2026-102631

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Patches & Fixes for CVE-2026-102631 (1)

Vendor Advisories for CVE-2026-102631 (2)

IV. Related Vulnerabilities

Same product: authd
Same vendor: Canonical
Same weakness: CWE-287

V. Comments for CVE-2026-102631

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