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CVE-2026-66883— Oidcc.Plug.Authorize user agent session binding inert due to case-sensitive header lookup

Quick assessment

Affected
Erlang Ecosystem Foundation oidcc_plug
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.

The Erlang Ecosystem Foundation Oidcc.Plug是The Erlang Ecosystem Foundation组织的一款身份认证插件。 The Erlang Ecosystem Foundation Oidcc.Plug 0.5.0之前版本存在输入验证错误漏洞，该漏洞源于大小写处理不当，导致Oidcc.Plug.Authorize模块在读取User-Agent请求头时未进行大小写归一化，将nil写入会话，使会话绑定检查失效，可能允许攻击者从不同用户代理完成授权回调而不

CVSS 6.3 · Medium EPSS 0.29% · P22

Possible ATT&CK Techniques 1 AI

T1528 · Steal Application Access Token

Affected Version Matrix 2

VendorProduct Version RangeStatus
Erlang Ecosystem Foundation oidcc_plug 0.1.0-alpha.3< 0.5.0 affected
0a75fb139d8e2686d1b75e0d48962323d2181673< f15e52c5750aaba701104b10ed96cfac063bd557 affected
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I. Basic Information for CVE-2026-66883

Vulnerability Information
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Vulnerability Title
Oidcc.Plug.Authorize user agent session binding inert due to case-sensitive header lookup
Source: CVE Program / CVE List V5
Vulnerability Description
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.
Source: CVE Program / CVE List V5
CVSS Information
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
Source: CVE Program / CVE List V5
Vulnerability Type
大小写敏感处理不恰当
Source: CVE Program / CVE List V5
Vulnerability Title
The Erlang Ecosystem Foundation Oidcc.Plug 输入验证错误漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
The Erlang Ecosystem Foundation Oidcc.Plug是The Erlang Ecosystem Foundation组织的一款身份认证插件。 The Erlang Ecosystem Foundation Oidcc.Plug 0.5.0之前版本存在输入验证错误漏洞，该漏洞源于大小写处理不当，导致Oidcc.Plug.Authorize模块在读取User-Agent请求头时未进行大小写归一化，将nil写入会话，使会话绑定检查失效，可能允许攻击者从不同用户代理完成授权回调而不
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
Erlang Ecosystem Foundation oidcc_plug 0.1.0-alpha.3 ~ 0.5.0 cpe:2.3:a:erlef:oidcc_plug:*:*:*:*:*:erlang:*:*
Erlang Ecosystem Foundation oidcc_plug 0a75fb139d8e2686d1b75e0d48962323d2181673 ~ f15e52c5750aaba701104b10ed96cfac063bd557 cpe:2.3:a:erlef:oidcc_plug:*:*:*:*:*:erlang:*:*

II. Public POCs for CVE-2026-66883

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III. Intelligence Information for CVE-2026-66883

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Patches & Fixes for CVE-2026-66883 (1)

Vendor Advisories for CVE-2026-66883 (2)

News Coverage for CVE-2026-66883 (1)

IV. Related Vulnerabilities

Same product: oidcc_plug
Same vendor: Erlang Ecosystem Foundation
Same weakness: CWE-178

V. Comments for CVE-2026-66883

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