CVE-2026-53424
Missing one-time-use enforcement in Samly allows replay of SAML bearer assertions
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 v0.3.0 onward.
INFO
Published Date :
Aug. 20, 2026, 6:16 p.m.
Last Modified :
Aug. 20, 2026, 6:16 p.m.
Remotely Exploit :
Yes !
Source :
6b3ad84c-e1a6-4bf7-a703-f496b71e49db
CVSS Scores
| Score | Version | Severity | Vector | Exploitability Score | Impact Score | Source |
|---|---|---|---|---|---|---|
| CVSS 4.0 | CRITICAL | 6b3ad84c-e1a6-4bf7-a703-f496b71e49db | ||||
| CVSS 4.0 | CRITICAL | 6b3ad84c-e1a6-4bf7-a703-f496b71e49db |
Solution
- Update Samly to a version that enforces assertion uniqueness.
- Implement or configure a duplicate assertion detector.
- Ensure SAML assertions are used only once.
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2026-53424.
| URL | Resource |
|---|---|
| https://cna.erlef.org/cves/CVE-2026-53424.html | |
| https://osv.dev/vulnerability/EEF-CVE-2026-53424 |
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2026-53424 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2026-53424
weaknesses.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2026-53424 vulnerability anywhere in the article.
The following table lists the changes that have been made to the
CVE-2026-53424 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
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New CVE Received by 6b3ad84c-e1a6-4bf7-a703-f496b71e49db
Aug. 20, 2026
Action Type Old Value New Value Added Affected [{'cpes': ['cpe:2.3:a:dropbox:samly:*:*:*:*:*:*:*:*'], 'repo': 'https://github.com/dropbox/samly', 'vendor': 'dropbox', 'modules': ["'Elixir.Samly.Helper'"], 'product': 'samly', 'versions': [{'status': 'affected', 'version': 'v0.3.0', 'lessThan': '*', 'versionType': 'semver'}], 'packageURL': 'pkg:hex/samly', 'packageName': 'samly', 'programFiles': ['lib/samly/helper.ex'], 'collectionURL': 'https://repo.hex.pm', 'defaultStatus': 'unaffected', 'programRoutines': [{'name': "'Elixir.Samly.Helper':decode_idp_auth_resp/3"}]}, {'cpes': ['cpe:2.3:a:dropbox:samly:*:*:*:*:*:*:*:*'], 'repo': 'https://github.com/dropbox/samly', 'vendor': 'dropbox', 'modules': ["'Elixir.Samly.Helper'"], 'product': 'samly', 'versions': [{'status': 'affected', 'version': '8a5bb1b4a4753d05470da2036323477f63cfdf4c', 'lessThan': '*', 'versionType': 'git'}], 'packageURL': 'pkg:github/dropbox/samly', 'packageName': 'dropbox/samly', 'programFiles': ['lib/samly/helper.ex'], 'collectionURL': 'https://github.com', 'defaultStatus': 'unaffected', 'programRoutines': [{'name': "'Elixir.Samly.Helper':decode_idp_auth_resp/3"}]}, {'cpes': ['cpe:2.3:a:handnot2:samly:*:*:*:*:*:*:*:*'], 'repo': 'https://github.com/handnot2/samly', 'vendor': 'handnot2', 'modules': ["'Elixir.Samly.Helper'"], 'product': 'samly', 'versions': [{'status': 'affected', 'version': '8a5bb1b4a4753d05470da2036323477f63cfdf4c', 'lessThan': '*', 'versionType': 'git'}], 'packageURL': 'pkg:github/handnot2/samly', 'packageName': 'handnot2/samly', 'programFiles': ['lib/samly/helper.ex'], 'collectionURL': 'https://github.com', 'defaultStatus': 'unaffected', 'programRoutines': [{'name': "'Elixir.Samly.Helper':decode_idp_auth_resp/3"}]}] Added 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 v0.3.0 onward. Added CVSS V4.0 AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X Added CWE CWE-294 Added Reference https://cna.erlef.org/cves/CVE-2026-53424.html Added Reference https://osv.dev/vulnerability/EEF-CVE-2026-53424