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CVE-2026-111056— FOSSBilling: Unauthenticated client account enumeration via guest signup endpoint

Quick assessment

Affected
FOSSBilling FOSSBilling
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.

FOSSBilling 是一个开源的账单与客户管理平台。在 0.1.0 至 0.8.7 版本中，未认证的 接口会暴露所提交的电子邮件是否属于已注册客户：当提交的邮箱地址已存在时，访客注册功能会返回一条未脱敏的独特错误信息。触发该漏洞的方式是向 接口发送包含目标邮箱地址的未认证请求。攻击者可以通过比较目标邮箱的访客注册响应，判断该邮箱是否属于现有的 FOSSBilling 客户。具体而言， 在 发现匹配记录后返回错误，而 API 响应直接暴露了该异常消息且未进行脱敏处理。此问题已在 0.8.7 版本中修复。

CVSS 6.9 · Medium

Affected Version Matrix 1

VendorProduct Version RangeStatus
FOSSBilling FOSSBilling >= 0.1.0, < 0.8.7 affected
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I. Basic Information for CVE-2026-111056

Vulnerability Information
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Vulnerability Title
FOSSBilling: Unauthenticated client account enumeration via guest signup endpoint
Source: CVE Program / CVE List V5
Vulnerability Description
FOSSBilling is an open source billing and client-management platform. From 0.1.0 until 0.8.7, the unauthenticated POST /api/guest/client/create endpoint reveals whether a submitted email belongs to a registered client because guest signup returns a distinct unredacted error when the submitted email already exists. The trigger is an unauthenticated request to POST /api/guest/client/create with a target email address. An attacker can compare the guest-signup response for a target email to determine whether the email belongs to an existing FOSSBilling client. Box\Mod\Client\Api\Guest::create returns the error after Client\Service::clientAlreadyExists finds a matching record, and the API response exposes that exception message without redaction. This issue is fixed in version 0.8.7.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N
Source: CVE Program / CVE List V5
Vulnerability Type
信息暴露
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
FOSSBilling FOSSBilling >= 0.1.0, < 0.8.7 -

II. Public POCs for CVE-2026-111056

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III. Intelligence Information for CVE-2026-111056

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Patches & Fixes for CVE-2026-111056 (2)

Vendor Advisories for CVE-2026-111056 (1)

Vendor Pages for CVE-2026-111056 (1)

Same Patch Batch · FOSSBilling · 2026-10-19 · 3 CVEs total

CVE-2026-111053 6.9 MEDIUM FOSSBilling: Unauthenticated attacker can probe existence of arbitrary files via guest/sys
CVE-2026-111046 2.3 LOW FOSSBilling: Low-privileged staff can read and modify configuration of deactivated extensi

IV. Related Vulnerabilities

Same product: FOSSBilling
Same vendor: FOSSBilling
Same weakness: CWE-200

V. Comments for CVE-2026-111056

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