CriticalCVE-2026-49757

    OAuth2/OIDC account takeover in AshAuthentication via email-based user matching (CVE-2026-49757)

    Published Last modified Sources: CVE.org, OSV, Hersteller

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    What is affected, what to do

    Authentication Bypass by Spoofing vulnerability in team-alembic AshAuthentication allows account takeover of local users via OAuth2/OIDC sign-in. AshAuthentication's OAuth2 and OIDC family strategies matched the local user by email address (an upsert on the email field, or a user-defined sign-in filter) rather than by the OpenID Connect iss/sub claim combination.

    Update Team-alembic Ash Authentication to version 4.14.0, Team-alembic Ash Authentication to version 5.0.0-rc.10.

    Affected
    • Team-alembic Ash Authentication lt 0.1.0..4.14.0
    • Team-alembic Ash Authentication lt 5.0.0-rc.0..5.0.0-rc.10
    Fixed in
    • Team-alembic Ash Authentication 4.14.0
    • Team-alembic Ash Authentication 5.0.0-rc.10

    Not sure whether and how you are affected? Ask a question about this vulnerability

    Metrics

    9.2

    Priority

    XIEM Effective CVSS: highest available CVSS rating from NVD and vendor data.

    Source: NVD, CVSS v4

    9.2

    CVSS v4

    Severity Critical on the scale from 0 to 10.

    Source: CVE.org, OSV, Hersteller

    0.6 %

    EPSS score

    Low — model estimates < 1% exploitation likelihood.

    Source: FIRST EPSS, percentile 49.6

    Show all metrics
    Severity
    Critical
    Priority (0–325)

    The priority score is a consolidated metric that condenses several individual signals into a single, action-guiding ranking: technical severity (CVSS), exploitation likelihood (EPSS), known-exploited status (KEV) and the context of the affected asset. The aim is to answer the only truly important question in vulnerability management: what first?

    Read in glossary
    84.29 Methodology
    Exploit maturity

    An exploit is code or a technique that specifically uses a concrete vulnerability to force unintended behaviour — such as executing code or escalating privileges. It is the tool that turns a theoretical flaw into a practical attack.

    Read in glossary
    no public PoC known
    XIEM Effective CVSS

    XIEM® is the tiered managed-security operating model from NEOSEC and a registered trademark of NEOSEC GmbH. It extends classic SIEM — the central collection, normalisation and correlation of security-relevant events — with endpoint forensics, network visibility and deception technology, and consolidates them into three building tiers: Sentry, Orchestrate and Command.

    Read in glossary
    9.2 Methodology
    CVSS v4

    CVSS is the globally established, open standard for assessing the technical severity of a vulnerability on a scale from 0 to 10. It describes how easily a flaw can be exploited and what damage it can cause — but not how likely its actual exploitation is. CVSS and the complementary EPSS deliberately answer different questions.

    Read in glossary
    9.2
    EPSS score

    The EPSS score is the absolute model output for an individual vulnerability: the estimated probability of real-world exploitation within the next 30 days, expressed as a value between 0 and 1 (i.e. 0 % to 100 %). A score of 0.42 means „the model estimates a 42 % chance of real-world exploitation within 30 days“.

    Read in glossary
    0.6 %
    Low — model estimates < 1% exploitation likelihood.
    EPSS percentile

    The EPSS percentile is the relative position of a vulnerability within all EPSS-scored CVEs, expressed as a value between 0 and 1. A percentile of 0.90 means „this CVE has a higher EPSS score than 90 % of all other scored CVEs“. Unlike the EPSS score, it is not a probability — but a positioning within a ranking.

    Read in glossary
    49.6
    High — this CVE ranks above the median of all CVEs scored today (rank ≥ 36%).
    KEV status

    The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching.

    Read in glossary
    —
    Published
    CISA assessment (SSVC)
    Exploitation: proof of concept · automatable · Technical impact: total
    Source: CISA Vulnrichment, as of 15 June 2026
    CWE

    CWE is a catalogue of typical weakness types in software and hardware — such as flawed input validation, unsafe memory handling or poor authentication. Where a CVE names a concrete vulnerability in a concrete product, a CWE describes the underlying class of defect.

    Read in glossary
    CWE-290

    Detection rules

    No NEOSEC detection rule is available for this vulnerability yet.

    Classification under NIS2 and CRA

    Rule-based classification from exploitation status and severity. It does not replace a case-by-case assessment.

    NIS2

    NIS2 is EU Directive (EU) 2022/2555 to raise the level of cybersecurity across the Union. It substantially broadens obligations compared with the first NIS directive: more sectors, mandatory risk management, staged reporting duties and personal accountability of senior management.

    Read in glossary
    High technical severity: assess and remediate the vulnerability in vulnerability handling under Art. 21(2)(e) NIS2 and document the decision.
    CRA

    The CRA is EU Regulation (EU) 2024/2847 setting horizontal cybersecurity requirements for „products with digital elements“ — from industrial controllers and software to connected consumer devices. For the first time manufacturers must ensure security across the entire product lifecycle, handle vulnerabilities and provide security updates.

    Read in glossary
    From 11.12.2027, Annex I Part II CRA requires manufacturers of affected products with digital elements to handle vulnerabilities without delay and provide security updates.
    ISO/IEC 27001

    ISO/IEC 27001 is the internationally leading standard for an information security management system (ISMS). It describes a risk-based, process-oriented framework to systematically plan, implement, review and improve information security.

    Read in glossary
    Control A.8.8, management of technical vulnerabilities: assess relevance to your systems, plan remediation and keep evidence.

    Description

    Authentication Bypass by Spoofing vulnerability in team-alembic AshAuthentication allows account takeover of local users via OAuth2/OIDC sign-in. AshAuthentication's OAuth2 and OIDC family strategies matched the local user by email address (an upsert on the email field, or a user-defined sign-in filter) rather than by the OpenID Connect iss/sub claim combination. Per OpenID Connect Core §5.7, only iss/sub uniquely and stably identifies an end-user; other claims, including email, MUST NOT be used as unique identifiers. A provider login presenting a victim's email, including an unverified email, a reused email, or an account with email_verified: false, resolved to and signed in as the victim's existing local account. An unauthenticated attacker who can register an account on any accepted OAuth provider with the victim's email (or who benefits from provider-side email reuse or reclamation) obtains the victim's full local privileges. The fix resolves users by the (strategy, sub) identity stored in a user identity resource, and only links a new sub to an existing local account by email when the provider's email_verified claim is trusted (trust_email_verified?). This issue affects ash_authentication from 0.1.0 before 4.14.0 and from 5.0.0-rc.0 before 5.0.0-rc.10.

    Source: NVD (NIST), CVE.org (MITRE), cvelistv5, OSV (Open Source Vulnerabilities), GitHub Security Advisories

    Affected products

    The following versions are affected. Older releases of the same product line are also vulnerable unless stated otherwise.

    Affected products
    Affected versionsFixed in
    team-alembicash_authentication
    • 5.0.0-rc.0 – < 5.0.0-rc.10
    • 0.1.0 – < 4.14.0
    • 5.0.0-rc.10
    • 4.14.0
    hexash_authentication
    • 3.9.4
    • 4.13.2
    • 4.9.6
    • 4.3.5
    • 4.7.1
    • 4.2.2
    • 4.9.9
    • 4.1.0
    • 4.3.3
    • 4.0.0-rc.1
    • 3.12.4
    • 4.2.7
    • 4.4.0
    • 4.0.0-rc.6
    • 3.5.2
    • 4.4.9
    • 4.13.5
    • 5.0.0-rc.5
    • 4.7.2
    • 3.10.0
    • 4.9.0
    • 4.6.4
    • 4.5.6
    • 4.3.2
    • 4.0.0-rc.5
    • 3.10.1
    • 4.8.2
    • 5.0.0-rc.7
    • 5.0.0-rc.6
    • 4.3.7
    • 4.6.2
    • 4.8.7
    • 4.6.3
    • 4.0.4
    • 3.9.6
    • 3.7.8
    • 3.2.1
    • 3.11.11
    • 4.8.6
    • 3.10.2
    • 4.9.1
    • 5.0.0-rc.3
    • 3.11.3
    • 3.11.14
    • 4.4.2
    • 3.12.1
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    Vendors and products

    Weakness classes (CWE)

    • CWE-290Authentication Bypass by Spoofing

      Base

      This attack-focused weakness is caused by incorrectly implemented authentication schemes that are subject to spoofing attacks.

      Entry at MITRE CWE-290

    References & sources

    • github.comteam-alembic/ash_authentication/security/advisories/GHSA-777c-2…advisory, Vendor advisory, related
    • cna.erlef.orgcves/CVE-2026-49757.htmlweb, related
    • github.comteam-alembic/ash_authentication/commit/728b8d28c1b5f465fa1116ef…fix, Patch
    • github.comteam-alembic/ash_authentication/commit/64530644f9b37ebb76ca14ae…fix, Patch
    • hex.pmpackages/ash_authenticationpackage
    • NVD (NIST)vuln/detail/CVE-2026-49757advisory
    • github.comteam-alembic/ash_authenticationpackage
    • github.comteam-alembic/ash_authentication/releases/tag/v4.14.0web
    • github.comteam-alembic/ash_authentication/releases/tag/v5.0.0-rc.10web
    • OSV (Open Source Vulnerabilities)vulnerability/EEF-CVE-2026-49757web, related

    Changes to this CVE

    Who changed this CVE and when: NVD (analysis, affected products, CVSS), the CVE publisher (CNA) and additional providers such as CISA (ADP).

    1. ReceivedEEF

      CVSS V4.0: AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N

      Weakness type: CWE-290

      Description added or changed

      Show 8 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Descriptionadded
      —
      Authentication Bypass by Spoofing vulnerability in team-alembic AshAuthentication allows account takeover of local users via OAuth2/OIDC sign-in. AshAuthentication's OAuth2 and OIDC family strategies matched the local user by email address (an upsert on the email field, or a user-defined sign-in filter) rather than by the OpenID Connect iss/sub claim combination. Per OpenID Connect Core §5.7, only iss/sub uniquely and stably identifies an end-user; other claims, including email, MUST NOT be used as unique identifiers. A provider login presenting a victim's email, including an unverified email, a reused email, or an account with email_verified: false, resolved to and signed in as the victim's existing local account. An unauthenticated attacker who can register an account on any accepted OAuth provider with the victim's email (or who benefits from provider-side email reuse or reclamation) obtains the victim's full local privileges. The fix resolves users by the (strategy, sub) identity stored in a user identity resource, and only links a new sub to an existing local account by email when the provider's email_verified claim is trusted (trust_email_verified?). This issue affects ash_authentication from 0.1.0 before 4.14.0 and from 5.0.0-rc.0 before 5.0.0-rc.10.
      CVSSadded
      —
      AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:H/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
      Weakness type (CWE)added
      —
      CWE-290
      Referenceadded
      —
      https://cna.erlef.org/cves/CVE-2026-49757.html
      Referenceadded
      —
      https://github.com/team-alembic/ash_authentication/commit/64530644f9b37ebb76ca14aeb83a77597a0034b7
      Referenceadded
      —
      https://github.com/team-alembic/ash_authentication/commit/728b8d28c1b5f465fa1116ef044a815300fc733d
      Referenceadded
      —
      https://github.com/team-alembic/ash_authentication/security/advisories/GHSA-777c-2fxx-qr28
      Referenceadded
      —
      https://osv.dev/vulnerability/EEF-CVE-2026-49757

      Source identifier: 6b3ad84c-e1a6-4bf7-a703-f496b71e49db

    One NVD translation into another language is hidden.

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