Oidcc.Plug.Authorize user agent session binding inert due to case-sensitive header lookup

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-66883
StatePUBLISHED
AssignerEEF
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-08-04 12:16:36 UTC
Updated2026-08-04 14:52:54 UTC
DescriptionImproper 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.

Risk And Classification

Primary CVSS: v4.0 6.3 MEDIUM from 6b3ad84c-e1a6-4bf7-a703-f496b71e49db

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/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

Problem Types: CWE-178 | CWE-178 CWE-178 Improper Handling of Case Sensitivity

VersionSourceTypeScoreSeverityVector
4.06b3ad84c-e1a6-4bf7-a703-f496b71e49dbSecondary6.3MEDIUMCVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/E:X/C...
4.0CNACVSS6.3MEDIUMCVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N

CVSS v4.0 Breakdown

Attack Vector
Network
Attack Complexity
High
Attack Requirements
Present
Privileges Required
None
User Interaction
None
Confidentiality
None
Integrity
Low
Availability
None
Sub Conf.
None
Sub Integrity
None
Sub Availability
None

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/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

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Erlang Ecosystem Foundation Oidcc Plug affected 0.1.0-alpha.3 0.5.0 semver Not specified
CNA Erlang Ecosystem Foundation Oidcc Plug affected 0a75fb139d8e2686d1b75e0d48962323d2181673 f15e52c5750aaba701104b10ed96cfac063bd557 git Not specified

References

ReferenceSourceLinkTags
cna.erlef.org/cves/CVE-2026-66883.html 6b3ad84c-e1a6-4bf7-a703-f496b71e49db cna.erlef.org
github.com/erlef/oidcc_plug/security/advisories/GHSA-w5r8-m75h-98fc 134c704f-9b21-4f2e-91b3-4a467353bcc0 github.com
osv.dev/vulnerability/EEF-CVE-2026-66883 6b3ad84c-e1a6-4bf7-a703-f496b71e49db osv.dev
github.com/erlef/oidcc_plug/commit/f15e52c5750aaba701104b10ed96cfac063bd557 6b3ad84c-e1a6-4bf7-a703-f496b71e49db github.com
CVE Program record CVE.ORG www.cve.org canonical
NVD vulnerability detail NVD nvd.nist.gov canonical, analysis

Vendor Comments And Credit

Discovery Credit

CNA: Mathias Polligkeit (en)

CNA: Jonatan Männchen / EEF (en)

CNA: Mathias Polligkeit (en)

CNA: Jonatan Männchen / EEF (en)

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