CVE-2026-66883Public exploitNetwork attack vector

Session-binding bypass via mixed-case header lookup

Published Aug 4, 2026 · Updated Aug 4, 2026

Improper case handling in Erlang Ecosystem Foundation oidcc_plug before 0.5.0 allows remote attackers to bypass session binding. Oidcc.Plug.Authorize.call/2 requests the mixed-case User-Agent key after Plug lowercases header names, stores nil, and lets the callback's nil branch return success without comparing clients. Exploitation requires a stolen session and check_useragent enabled; CSRF/state, nonce, PKCE, and peer-IP checks remain effective.

CVSS severity6.3
Medium
EPSS probability0.29%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper case handling in Erlang Ecosystem Foundation oidcc_plug before 0.5.0 allows remote attackers to bypass session binding. Oidcc.Plug.Authorize.call/2 requests the mixed-case User-Agent key after Plug lowercases header names, stores nil, and lets the callback's nil branch return success without comparing clients. Exploitation requires a stolen session and check_useragent enabled; CSRF/state, nonce, PKCE, and peer-IP checks remain effective.

The record

CVE
CVE-2026-66883
Published
Aug 4, 2026
Updated
Aug 4, 2026
Vendor
Erlang Ecosystem Foundation
Product
oidcc_plug
Classifications
CWE-178, CAPEC-60, T1550.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 4, 2026CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=0.1.0-alpha.3 <0.5.0
  2. Affected versionversion=0a75fb139d8e2686d1b75e0d48962323d2181673 <f15e52c5750aaba701104b10ed96cfac063bd557

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Erlang Ecosystem Foundation · oidcc_plugversion=0.1.0-alpha.3 <0.5.0; version=0a75fb139d8e2686d1b75e0d48962323d2181673 <f15e52c5750aaba701104b10ed96cfac063bd557

Published CVSS scores

6.3Erlang Ecosystem FoundationCVSS: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 describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-178Improper Handling of Case Sensitivity
CAPEC-60Reusing Session IDs (aka Session Replay)
T1550.004Web Session Cookie

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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