CVE-2026-53424 (GCVE-0-2026-53424)
Vulnerability from cvelistv5 – Published: 2026-08-20 17:27 – Updated: 2026-08-21 19:42
VLAI
EPSS
VEX
Title
Missing one-time-use enforcement in Samly allows replay of SAML bearer assertions
Summary
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.
Severity
SSVC
Exploitation: none
Automatable: yes
Technical Impact: total
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-08-21 19:41 UTC
CWE
- CWE-294 - Authentication Bypass by Capture-replay
Assigner
References
2 references
| URL | Tags |
|---|---|
| https://cna.erlef.org/cves/CVE-2026-53424.html | relatedthird-party-advisory |
| https://osv.dev/vulnerability/EEF-CVE-2026-53424 | related |
Impacted products
3 products
| Vendor | Product | Version | CPE status | |
|---|---|---|---|---|
| dropbox | samly |
Affected:
0.3.0 , < *
(semver)
cpe:2.3:a:dropbox:samly:*:*:*:*:*:*:*:* |
||
| dropbox | samly |
Affected:
8a5bb1b4a4753d05470da2036323477f63cfdf4c , < *
(git)
cpe:2.3:a:dropbox:samly:*:*:*:*:*:*:*:* |
||
| handnot2 | samly |
Affected:
8a5bb1b4a4753d05470da2036323477f63cfdf4c , < *
(git)
cpe:2.3:a:handnot2:samly:*:*:*:*:*:*:*:* |
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"value": "\u003cp\u003eAuthentication Bypass by Capture-replay vulnerability in dropbox samly allows an attacker to authenticate as the subject of a captured SAML assertion by resubmitting it.\u003c/p\u003e\n\u003cp\u003e\u003ccode\u003eSamly.Helper.decode_idp_auth_resp/3\u003c/code\u003e in \u003ccode\u003elib/samly/helper.ex\u003c/code\u003e calls \u003ccode\u003eesaml_sp:validate_assertion/2\u003c/code\u003e, whose default duplicate detector is a no-op. The \u003ccode\u003e/3\u003c/code\u003e arity accepting a \u003ccode\u003eDuplicateFun\u003c/code\u003e exists in \u003ccode\u003eesaml\u003c/code\u003e 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 \u003ccode\u003eSAMLResponse\u003c/code\u003e obtained from the network, from browser history, or from logs can submit the identical bytes repeatedly until the assertion\u0027s \u003ccode\u003eNotOnOrAfter\u003c/code\u003e passes, each time establishing a session as the assertion\u0027s subject.\u003c/p\u003e\n\u003cp\u003eThis issue affects samly: from 0.3.0 onward.\u003c/p\u003e"
},
{
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"type": "text/markdown",
"value": "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.\n\n`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\u0027s `NotOnOrAfter` passes, each time establishing a session as the assertion\u0027s subject.\n\nThis issue affects samly: from 0.3.0 onward."
}
],
"value": "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.\n\nSamly.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\u0027s NotOnOrAfter passes, each time establishing a session as the assertion\u0027s subject.\n\nThis issue affects samly: from 0.3.0 onward."
}
],
"impacts": [
{
"capecId": "CAPEC-60",
"descriptions": [
{
"lang": "en",
"value": "CAPEC-60 Reusing Session IDs (aka Session Replay)"
}
]
}
],
"metrics": [
{
"cvssV4_0": {
"Automatable": "NOT_DEFINED",
"Recovery": "NOT_DEFINED",
"Safety": "NOT_DEFINED",
"attackComplexity": "LOW",
"attackRequirements": "PRESENT",
"attackVector": "NETWORK",
"baseScore": 9.1,
"baseSeverity": "CRITICAL",
"privilegesRequired": "NONE",
"providerUrgency": "NOT_DEFINED",
"subAvailabilityImpact": "NONE",
"subConfidentialityImpact": "NONE",
"subIntegrityImpact": "NONE",
"userInteraction": "NONE",
"valueDensity": "NOT_DEFINED",
"vectorString": "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",
"version": "4.0",
"vulnAvailabilityImpact": "NONE",
"vulnConfidentialityImpact": "HIGH",
"vulnIntegrityImpact": "HIGH",
"vulnerabilityResponseEffort": "NOT_DEFINED"
},
"format": "CVSS",
"scenarios": [
{
"lang": "en",
"value": "GENERAL"
}
]
}
],
"problemTypes": [
{
"descriptions": [
{
"cweId": "CWE-294",
"description": "CWE-294 Authentication Bypass by Capture-replay",
"lang": "en",
"type": "CWE"
}
]
}
],
"providerMetadata": {
"dateUpdated": "2026-08-20T18:37:24.439Z",
"orgId": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db",
"shortName": "EEF"
},
"references": [
{
"tags": [
"related",
"third-party-advisory"
],
"url": "https://cna.erlef.org/cves/CVE-2026-53424.html"
},
{
"tags": [
"related"
],
"url": "https://osv.dev/vulnerability/EEF-CVE-2026-53424"
}
],
"source": {
"discovery": "UNKNOWN"
},
"title": "Missing one-time-use enforcement in Samly allows replay of SAML bearer assertions"
}
},
"cveMetadata": {
"assignerOrgId": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db",
"assignerShortName": "EEF",
"cveId": "CVE-2026-53424",
"datePublished": "2026-08-20T17:27:11.115Z",
"dateReserved": "2026-06-09T11:01:47.529Z",
"dateUpdated": "2026-08-21T19:42:21.623Z",
"state": "PUBLISHED"
},
"dataType": "CVE_RECORD",
"dataVersion": "5.2"
}
}
}
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Experimental. This forecast is provided for visualization only and may change without notice. Do not use it for operational decisions.
Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.
Sightings
| Author | Source | Type | Date | Other |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or observed by the user.
- Confirmed: The vulnerability has been validated from an analyst's perspective.
- Published Proof of Concept: A public proof of concept is available for this vulnerability.
- Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
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- Not confirmed: The user expressed doubt about the validity of the vulnerability.
- Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.
Vulnerability timeline
Sightings and recorded dates, grouped by day · UTC
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The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the
vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base
model, served locally by ML-Gateway.
They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.
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Related by attack behaviour
Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.