CVE-2026-66883 (GCVE-0-2026-66883)
Vulnerability from cvelistv5 – Published: 2026-08-04 11:46 – Updated: 2026-08-04 12:27
VLAI
EPSS
VEX
Title
Oidcc.Plug.Authorize user agent session binding inert due to case-sensitive header lookup
Summary
Improper Handling of Case Sensitivity vulnerability in Erlang Ecosystem Foundation oidcc_plug (Oidcc.Plug.Authorize module) renders the user agent session binding inert, removing a defense in depth control against replay of a stolen session.
This vulnerability is associated with program files lib/oidcc/plug/authorize.ex and lib/oidcc/plug/authorization_callback.ex, and program routines Oidcc.Plug.Authorize.call/2 and Oidcc.Plug.AuthorizationCallback.call/2.
Oidcc.Plug.Authorize.call/2 reads the initiating client's user agent with get_req_header(conn, "User-Agent"). Plug lowercases incoming header names, but get_req_header/2 matches the supplied key exactly and performs no normalization of its own, so the mixed-case lookup always returns an empty list and nil is written into the session. On the callback side, Oidcc.Plug.AuthorizationCallback treats a stored nil user agent as nothing to compare and returns :ok without inspecting the request. The two behaviours combine so that the check passes unconditionally on every request, including for deployments that explicitly opted in with check_useragent: true, and an authorization callback can be completed from a different user agent than the one that initiated the flow without detection. The check fails open silently, with no error and no log entry, so a deployment cannot tell the binding is absent.
The impact is limited to defense in depth. The inert check does not by itself allow an attacker to complete an authorization flow; it removes one layer that would otherwise hinder use of a stolen or leaked session, such as an exfiltrated session cookie replayed from a different client. The CSRF/state, nonce, and PKCE checks are unaffected and continue to function. Deployments that never enabled check_useragent are not affected in practice, since they never expected the binding. The corresponding lookup in Oidcc.Plug.AuthorizationCallback correctly uses the lowercase key and is not affected.
This issue affects oidcc_plug: from 0.1.0-alpha.3 before 0.5.0.
Severity
SSVC
Exploitation: poc
Automatable: no
Technical Impact: partial
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-08-04 12:27 UTC
CWE
- CWE-178 - Improper Handling of Case Sensitivity
Assigner
References
4 references
| URL | Tags |
|---|---|
| https://github.com/erlef/oidcc_plug/security/advi… | vendor-advisoryrelated |
| https://cna.erlef.org/cves/CVE-2026-66883.html | related |
| https://osv.dev/vulnerability/EEF-CVE-2026-66883 | related |
| https://github.com/erlef/oidcc_plug/commit/f15e52… | patch |
Impacted products
2 products
| Vendor | Product | Version | CPE status | |
|---|---|---|---|---|
| Erlang Ecosystem Foundation | oidcc_plug |
Affected:
0.1.0-alpha.3 , < 0.5.0
(semver)
cpe:2.3:a:erlef:oidcc_plug:*:*:*:*:*:erlang:*:* |
||
| Erlang Ecosystem Foundation | oidcc_plug |
Affected:
0a75fb139d8e2686d1b75e0d48962323d2181673 , < f15e52c5750aaba701104b10ed96cfac063bd557
(git)
cpe:2.3:a:erlef:oidcc_plug:*:*:*:*:*:erlang:*:* |
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"source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
"url": "https://github.com/erlef/oidcc_plug/security/advisories/GHSA-w5r8-m75h-98fc"
}
],
"sourceIdentifier": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db",
"vulnStatus": "Awaiting Analysis",
"weaknesses": [
{
"description": [
{
"lang": "en",
"value": "CWE-178"
}
],
"source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db",
"type": "Secondary"
}
]
}
},
"vulnrichment": {
"containers": {
"adp": [
{
"metrics": [
{
"other": {
"content": {
"id": "CVE-2026-66883",
"options": [
{
"Exploitation": "poc"
},
{
"Automatable": "no"
},
{
"Technical Impact": "partial"
}
],
"role": "CISA Coordinator",
"timestamp": "2026-08-04T12:27:16.535019Z",
"version": "2.0.3"
},
"type": "ssvc"
}
}
],
"providerMetadata": {
"dateUpdated": "2026-08-04T12:27:37.541Z",
"orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
"shortName": "CISA-ADP"
},
"references": [
{
"tags": [
"exploit"
],
"url": "https://github.com/erlef/oidcc_plug/security/advisories/GHSA-w5r8-m75h-98fc"
}
],
"title": "CISA ADP Vulnrichment"
}
],
"cna": {
"affected": [
{
"collectionURL": "https://repo.hex.pm",
"cpes": [
"cpe:2.3:a:erlef:oidcc_plug:*:*:*:*:*:erlang:*:*"
],
"defaultStatus": "unaffected",
"modules": [
"Elixir.Oidcc.Plug.Authorize",
"Elixir.Oidcc.Plug.AuthorizationCallback"
],
"packageName": "oidcc_plug",
"packageURL": "pkg:hex/oidcc_plug",
"product": "oidcc_plug",
"programFiles": [
"lib/oidcc/plug/authorize.ex",
"lib/oidcc/plug/authorization_callback.ex"
],
"programRoutines": [
{
"name": "\u0027Elixir.Oidcc.Plug.Authorize\u0027:call/2"
},
{
"name": "\u0027Elixir.Oidcc.Plug.AuthorizationCallback\u0027:call/2"
}
],
"repo": "https://github.com/erlef/oidcc_plug",
"vendor": "Erlang Ecosystem Foundation",
"versions": [
{
"lessThan": "0.5.0",
"status": "affected",
"version": "0.1.0-alpha.3",
"versionType": "semver"
}
]
},
{
"collectionURL": "https://github.com",
"cpes": [
"cpe:2.3:a:erlef:oidcc_plug:*:*:*:*:*:erlang:*:*"
],
"defaultStatus": "unaffected",
"modules": [
"Elixir.Oidcc.Plug.Authorize",
"Elixir.Oidcc.Plug.AuthorizationCallback"
],
"packageName": "erlef/oidcc_plug",
"packageURL": "pkg:github/erlef/oidcc_plug",
"product": "oidcc_plug",
"programFiles": [
"lib/oidcc/plug/authorize.ex",
"lib/oidcc/plug/authorization_callback.ex"
],
"programRoutines": [
{
"name": "\u0027Elixir.Oidcc.Plug.Authorize\u0027:call/2"
},
{
"name": "\u0027Elixir.Oidcc.Plug.AuthorizationCallback\u0027:call/2"
}
],
"repo": "https://github.com/erlef/oidcc_plug",
"vendor": "Erlang Ecosystem Foundation",
"versions": [
{
"lessThan": "f15e52c5750aaba701104b10ed96cfac063bd557",
"status": "affected",
"version": "0a75fb139d8e2686d1b75e0d48962323d2181673",
"versionType": "git"
}
]
}
],
"cpeApplicability": [
{
"nodes": [
{
"cpeMatch": [
{
"criteria": "cpe:2.3:a:erlef:oidcc_plug:*:*:*:*:*:erlang:*:*",
"versionEndExcluding": "0.5.0",
"versionStartIncluding": "0.1.0-alpha.3",
"vulnerable": true
}
],
"negate": false,
"operator": "OR"
}
],
"operator": "AND"
}
],
"credits": [
{
"lang": "en",
"type": "finder",
"value": "Mathias Polligkeit"
},
{
"lang": "en",
"type": "remediation developer",
"value": "Jonatan M\u00e4nnchen / EEF"
},
{
"lang": "en",
"type": "remediation reviewer",
"value": "Mathias Polligkeit"
},
{
"lang": "en",
"type": "coordinator",
"value": "Jonatan M\u00e4nnchen / EEF"
}
],
"descriptions": [
{
"lang": "en",
"supportingMedia": [
{
"base64": false,
"type": "text/html",
"value": "\u003cp\u003eImproper Handling of Case Sensitivity vulnerability in Erlang Ecosystem Foundation oidcc_plug (\u003ccode\u003eOidcc.Plug.Authorize\u003c/code\u003e module) renders the user agent session binding inert, removing a defense in depth control against replay of a stolen session.\u003c/p\u003e\n\u003cp\u003eThis vulnerability is associated with program files \u003ccode\u003elib/oidcc/plug/authorize.ex\u003c/code\u003e and \u003ccode\u003elib/oidcc/plug/authorization_callback.ex\u003c/code\u003e, and program routines \u003ccode\u003eOidcc.Plug.Authorize.call/2\u003c/code\u003e and \u003ccode\u003eOidcc.Plug.AuthorizationCallback.call/2\u003c/code\u003e.\u003c/p\u003e\n\u003cp\u003e\u003ccode\u003eOidcc.Plug.Authorize.call/2\u003c/code\u003e reads the initiating client\u0027s user agent with \u003ccode\u003eget_req_header(conn, \"User-Agent\")\u003c/code\u003e. Plug lowercases incoming header names, but \u003ccode\u003eget_req_header/2\u003c/code\u003e matches the supplied key exactly and performs no normalization of its own, so the mixed-case lookup always returns an empty list and \u003ccode\u003enil\u003c/code\u003e is written into the session. On the callback side, \u003ccode\u003eOidcc.Plug.AuthorizationCallback\u003c/code\u003e treats a stored \u003ccode\u003enil\u003c/code\u003e user agent as nothing to compare and returns \u003ccode\u003e:ok\u003c/code\u003e without inspecting the request. The two behaviours combine so that the check passes unconditionally on every request, including for deployments that explicitly opted in with \u003ccode\u003echeck_useragent: true\u003c/code\u003e, and an authorization callback can be completed from a different user agent than the one that initiated the flow without detection. The check fails open silently, with no error and no log entry, so a deployment cannot tell the binding is absent.\u003c/p\u003e\n\u003cp\u003eThe impact is limited to defense in depth. The inert check does not by itself allow an attacker to complete an authorization flow; it removes one layer that would otherwise hinder use of a stolen or leaked session, such as an exfiltrated session cookie replayed from a different client. The CSRF/state, nonce, and PKCE checks are unaffected and continue to function. Deployments that never enabled \u003ccode\u003echeck_useragent\u003c/code\u003e are not affected in practice, since they never expected the binding. The corresponding lookup in \u003ccode\u003eOidcc.Plug.AuthorizationCallback\u003c/code\u003e correctly uses the lowercase key and is not affected.\u003c/p\u003e\n\u003cp\u003eThis issue affects oidcc_plug: from 0.1.0-alpha.3 before 0.5.0.\u003c/p\u003e"
},
{
"base64": false,
"type": "text/markdown",
"value": "Improper Handling of Case Sensitivity vulnerability in Erlang Ecosystem Foundation oidcc_plug (`Oidcc.Plug.Authorize` module) renders the user agent session binding inert, removing a defense in depth control against replay of a stolen session.\n\nThis vulnerability is associated with program files `lib/oidcc/plug/authorize.ex` and `lib/oidcc/plug/authorization_callback.ex`, and program routines `Oidcc.Plug.Authorize.call/2` and `Oidcc.Plug.AuthorizationCallback.call/2`.\n\n`Oidcc.Plug.Authorize.call/2` reads the initiating client\u0027s user agent with `get_req_header(conn, \"User-Agent\")`. Plug lowercases incoming header names, but `get_req_header/2` matches the supplied key exactly and performs no normalization of its own, so the mixed-case lookup always returns an empty list and `nil` is written into the session. On the callback side, `Oidcc.Plug.AuthorizationCallback` treats a stored `nil` user agent as nothing to compare and returns `:ok` without inspecting the request. The two behaviours combine so that the check passes unconditionally on every request, including for deployments that explicitly opted in with `check_useragent: true`, and an authorization callback can be completed from a different user agent than the one that initiated the flow without detection. The check fails open silently, with no error and no log entry, so a deployment cannot tell the binding is absent.\n\nThe impact is limited to defense in depth. The inert check does not by itself allow an attacker to complete an authorization flow; it removes one layer that would otherwise hinder use of a stolen or leaked session, such as an exfiltrated session cookie replayed from a different client. The CSRF/state, nonce, and PKCE checks are unaffected and continue to function. Deployments that never enabled `check_useragent` are not affected in practice, since they never expected the binding. The corresponding lookup in `Oidcc.Plug.AuthorizationCallback` correctly uses the lowercase key and is not affected.\n\nThis issue affects oidcc_plug: from 0.1.0-alpha.3 before 0.5.0."
}
],
"value": "Improper Handling of Case Sensitivity vulnerability in Erlang Ecosystem Foundation oidcc_plug (Oidcc.Plug.Authorize module) renders the user agent session binding inert, removing a defense in depth control against replay of a stolen session.\n\nThis vulnerability is associated with program files lib/oidcc/plug/authorize.ex and lib/oidcc/plug/authorization_callback.ex, and program routines Oidcc.Plug.Authorize.call/2 and Oidcc.Plug.AuthorizationCallback.call/2.\n\nOidcc.Plug.Authorize.call/2 reads the initiating client\u0027s user agent with get_req_header(conn, \"User-Agent\"). Plug lowercases incoming header names, but get_req_header/2 matches the supplied key exactly and performs no normalization of its own, so the mixed-case lookup always returns an empty list and nil is written into the session. On the callback side, Oidcc.Plug.AuthorizationCallback treats a stored nil user agent as nothing to compare and returns :ok without inspecting the request. The two behaviours combine so that the check passes unconditionally on every request, including for deployments that explicitly opted in with check_useragent: true, and an authorization callback can be completed from a different user agent than the one that initiated the flow without detection. The check fails open silently, with no error and no log entry, so a deployment cannot tell the binding is absent.\n\nThe impact is limited to defense in depth. The inert check does not by itself allow an attacker to complete an authorization flow; it removes one layer that would otherwise hinder use of a stolen or leaked session, such as an exfiltrated session cookie replayed from a different client. The CSRF/state, nonce, and PKCE checks are unaffected and continue to function. Deployments that never enabled check_useragent are not affected in practice, since they never expected the binding. The corresponding lookup in Oidcc.Plug.AuthorizationCallback correctly uses the lowercase key and is not affected.\n\nThis issue affects oidcc_plug: from 0.1.0-alpha.3 before 0.5.0."
}
],
"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": "HIGH",
"attackRequirements": "PRESENT",
"attackVector": "NETWORK",
"baseScore": 6.3,
"baseSeverity": "MEDIUM",
"privilegesRequired": "NONE",
"providerUrgency": "NOT_DEFINED",
"subAvailabilityImpact": "NONE",
"subConfidentialityImpact": "NONE",
"subIntegrityImpact": "NONE",
"userInteraction": "NONE",
"valueDensity": "NOT_DEFINED",
"vectorString": "CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N",
"version": "4.0",
"vulnAvailabilityImpact": "NONE",
"vulnConfidentialityImpact": "NONE",
"vulnIntegrityImpact": "LOW",
"vulnerabilityResponseEffort": "NOT_DEFINED"
},
"format": "CVSS",
"scenarios": [
{
"lang": "en",
"value": "GENERAL"
}
]
}
],
"problemTypes": [
{
"descriptions": [
{
"cweId": "CWE-178",
"description": "CWE-178 Improper Handling of Case Sensitivity",
"lang": "en",
"type": "CWE"
}
]
}
],
"providerMetadata": {
"dateUpdated": "2026-08-04T11:46:05.191Z",
"orgId": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db",
"shortName": "EEF"
},
"references": [
{
"tags": [
"vendor-advisory",
"related"
],
"url": "https://github.com/erlef/oidcc_plug/security/advisories/GHSA-w5r8-m75h-98fc"
},
{
"tags": [
"related"
],
"url": "https://cna.erlef.org/cves/CVE-2026-66883.html"
},
{
"tags": [
"related"
],
"url": "https://osv.dev/vulnerability/EEF-CVE-2026-66883"
},
{
"tags": [
"patch"
],
"url": "https://github.com/erlef/oidcc_plug/commit/f15e52c5750aaba701104b10ed96cfac063bd557"
}
],
"source": {
"discovery": "EXTERNAL"
},
"title": "Oidcc.Plug.Authorize user agent session binding inert due to case-sensitive header lookup"
}
},
"cveMetadata": {
"assignerOrgId": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db",
"assignerShortName": "EEF",
"cveId": "CVE-2026-66883",
"datePublished": "2026-08-04T11:46:05.191Z",
"dateReserved": "2026-07-28T04:15:10.240Z",
"dateUpdated": "2026-08-04T12:27:58.024Z",
"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.
- Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
- Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
- 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.
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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.
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