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CVE-2026-53424— Missing one-time-use enforcement in Samly allows replay of SAML bearer assertions

Quick assessment

Affected
dropbox samly
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.

Dropbox Samly 中存在通过重放捕获数据绕过身份验证的漏洞，攻击者可以通过重新提交捕获到的 SAML 断言，以该断言所指代的主体身份完成身份验证。 Samly.Helper.decode_idp_auth_resp/3（位于 lib/samly/helper.ex）会调用 esaml_sp:validate_assertion/2。该函数的默认重复检测器是一个空操作（no-op）。虽然 esaml 中提供了接受 DuplicateFun 参数的 /3 元数版本，并实现了相应的重复检查逻辑，但 Samly

CVSS 9.1 · Critical EPSS 0.34% · P27

Affected Version Matrix 3

VendorProduct Version RangeStatus
dropbox samly 0.3.0< * affected
8a5bb1b4a4753d05470da2036323477f63cfdf4c< * affected
handnot2 samly 8a5bb1b4a4753d05470da2036323477f63cfdf4c< * affected
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I. Basic Information for CVE-2026-53424

Vulnerability Information
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Vulnerability Title
Missing one-time-use enforcement in Samly allows replay of SAML bearer assertions
Source: CVE Program / CVE List V5
Vulnerability Description
Authentication Bypass by Capture-replay vulnerability in dropbox samly allows an attacker to authenticate as the subject of a captured SAML assertion by resubmitting it. Samly.Helper.decode_idp_auth_resp/3 in lib/samly/helper.ex calls esaml_sp:validate_assertion/2, whose default duplicate detector is a no-op. The /3 arity accepting a DuplicateFun exists in esaml and implements the check, but Samly never calls it and offers no configuration to supply one, so the SAML 2.0 Web Browser SSO Profile requirement that a bearer assertion be used once is unenforced. An attacker holding a valid SAMLResponse obtained from the network, from browser history, or from logs can submit the identical bytes repeatedly until the assertion's NotOnOrAfter passes, each time establishing a session as the assertion's subject. This issue affects samly: from 0.3.0 onward.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N
Source: CVE Program / CVE List V5
Vulnerability Type
使用捕获-重放进行的认证绕过
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
dropbox samly 0.3.0 ~ * cpe:2.3:a:dropbox:samly:*:*:*:*:*:*:*:*
dropbox samly 8a5bb1b4a4753d05470da2036323477f63cfdf4c ~ * cpe:2.3:a:dropbox:samly:*:*:*:*:*:*:*:*
handnot2 samly 8a5bb1b4a4753d05470da2036323477f63cfdf4c ~ * cpe:2.3:a:handnot2:samly:*:*:*:*:*:*:*:*

II. Public POCs for CVE-2026-53424

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III. Intelligence Information for CVE-2026-53424

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Vendor Advisories for CVE-2026-53424 (1)

IV. Related Vulnerabilities

Same product: samly
Same vendor: dropbox
Same weakness: CWE-294

V. Comments for CVE-2026-53424

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