CriticalCVE-2026-55518

    Avo: Authorization Bypass Through User-Controlled Key (CVE-2026-55518)

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

    What is affected, what to do

    Avo is a framework to create admin panels for Ruby on Rails apps. Prior to 3.32.1 and 4.0.0.beta.51, Avo's association attach workflow checks attach_<association>? in the UI and GET /resources/:resource/:id/:related/new path, but the actual write endpoint, POST /resources/:resource/:id/:related, does not run the same authorization check before mutating the association through Avo::AssociationsController#create.

    Update Avo to version 3.32.1.

    Affected
    • Avo gte 4.0.0.beta.1, < 4.0.0.beta.51..*
    • Avo lt *..3.32.1
    Fixed in
    • Avo 3.32.1

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

    Metrics

    9.6

    Priority

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

    Source: NVD, CVSS v3

    9.6

    CVSS v3

    Severity Critical on the scale from 0 to 10.

    Source: OSV, Hersteller, CVE.org

    0.4 %

    EPSS score

    Low — model estimates < 1% exploitation likelihood.

    Source: FIRST EPSS, percentile 35.1

    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
    80.81 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
    9.6 Methodology
    CVSS v3

    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
    9.6
    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
    0.4 %
    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
    35.1
    Elevated — this CVE ranks above at least 10% of all CVEs scored today.
    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
    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-639, CWE-862, CWE-863

    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

    Avo is a framework to create admin panels for Ruby on Rails apps. Prior to 3.32.1 and 4.0.0.beta.51, Avo's association attach workflow checks attach_<association>? in the UI and GET /resources/:resource/:id/:related/new path, but the actual write endpoint, POST /resources/:resource/:id/:related, does not run the same authorization check before mutating the association through Avo::AssociationsController#create. An authenticated low-privileged Avo user can bypass hidden or disabled attach controls and directly attach related records to a parent record by sending a crafted POST request, which can lead to privilege escalation and cross-tenant data exposure where associations represent authorization-bearing relationships. This issue is fixed in versions 3.32.1 and 4.0.0.beta.51.

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

    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
    avo-hqavo
    • < 3.32.1
    • ≥ 4.0.0.beta.1, < 4.0.0.beta.51
    • 3.32.1
    • —
    rubygemsavo
    • 4.0.0.beta.16
    • 3.14.2
    • 1.13.2
    • 4.0.0.beta.38
    • 3.1.6
    • 1.10.3
    • 3.17.4.tw4
    • 2.32.0
    • 2.17.1.pre.1.zeitwerk.eager.load.dir
    • 1.11.6
    • 0.2.2
    • 2.9.1.pre2
    • 1.22.4
    • 3.11.2
    • 1.18.0.pre.3
    • 0.4.3
    • 1.2.11.pre.2
    • 2.26.0
    • 1.0.0
    • 0.5.0.beta9
    • 0.5.0.beta14
    • 2.14.3.pre.1.branding
    • 1.4.4.pre.1
    • 4.0.0.beta.20
    • 3.17.1
    • 3.10.10
    • 2.9.0
    • 4.0.0.beta.10
    • 2.10.0
    • 3.1.0
    • 4.0.0.beta.17
    • 3.7.4
    • 3.5.1
    • 3.26.0
    • 2.30.0
    • 1.5.4
    • 1.5.2
    • 1.24.0
    • 1.21.0.pre.1
    • 2.3.1.pre.5
    • 2.26.2.pre.pr1579
    • 1.11.5
    • 4.0.0.beta.5
    • 2.24.0
    • 4.0.0.beta.50
    • 3.32.0
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    Vendors and products

    Weakness classes (CWE)

    • CWE-639Authorization Bypass Through User-Controlled Key

      Base

      The system's authorization functionality does not prevent one user from gaining access to another user's data or record by modifying the key value identifying the data.

      Entry at MITRE CWE-639

    • CWE-862Missing Authorization

      Class

      The product does not perform an authorization check when an actor attempts to access a resource or perform an action.

      Entry at MITRE CWE-862

    • CWE-863Incorrect Authorization

      Class

      The product performs an authorization check when an actor attempts to access a resource or perform an action, but it does not correctly perform the check.

      Entry at MITRE CWE-863

    References & sources

    • github.comavo-hq/avo/security/advisories/GHSA-8fq9-273g-6mrgweb, x_refsource_CONFIRM
    • NVD (NIST)vuln/detail/CVE-2026-55518advisory
    • github.comavo-hq/avo/pull/4568web, x_refsource_MISC
    • github.comavo-hq/avo/commit/995928e586fd1788dd496bd51c4dbe4a79cb2b9cweb, x_refsource_MISC
    • github.comavo-hq/avopackage
    • github.comavo-hq/avo/releases/tag/v3.32.1web, x_refsource_MISC
    • github.comrubysec/ruby-advisory-db/blob/master/gems/avo/CVE-2026-55518.ymlweb
    • CVE.org (MITRE)CVERecord?id=CVE-2026-55518web

    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. Record modifiedCISA ADP

      CISA assessment (SSVC): exploitation: proof of concept, automatable: no

      Show 2 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Referenceadded
      —
      https://github.com/avo-hq/avo/security/advisories/GHSA-8fq9-273g-6mrg
      SSVC assessmentadded
      —
      {"id":"CVE-2026-55518","role":"CISA Coordinator","options":[{"exploitation":"poc"},{"automatable":"no"},{"technicalImpact":"total"}],"version":"2.0.3","timestamp":"2026-07-20T15:18:54.194227Z"}

      Source identifier: 134c704f-9b21-4f2e-91b3-4a467353bcc0

    2. ReceivedGitHub

      CVSS V3.1: AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:N

      Weakness type: CWE-639, CWE-862, CWE-863

      Description added or changed

      Show 10 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Affected versions (publisher)added
      —
      avo
      Descriptionadded
      —
      Avo is a framework to create admin panels for Ruby on Rails apps. Prior to 3.32.1 and 4.0.0.beta.51, Avo's association attach workflow checks attach_<association>? in the UI and GET /resources/:resource/:id/:related/new path, but the actual write endpoint, POST /resources/:resource/:id/:related, does not run the same authorization check before mutating the association through Avo::AssociationsController#create. An authenticated low-privileged Avo user can bypass hidden or disabled attach controls and directly attach related records to a parent record by sending a crafted POST request, which can lead to privilege escalation and cross-tenant data exposure where associations represent authorization-bearing relationships. This issue is fixed in versions 3.32.1 and 4.0.0.beta.51.
      CVSSadded
      —
      AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:N
      Weakness type (CWE)added
      —
      CWE-639
      Weakness type (CWE)added
      —
      CWE-862
      Weakness type (CWE)added
      —
      CWE-863
      Referenceadded
      —
      https://github.com/avo-hq/avo/commit/995928e586fd1788dd496bd51c4dbe4a79cb2b9c
      Referenceadded
      —
      https://github.com/avo-hq/avo/pull/4568
      Referenceadded
      —
      https://github.com/avo-hq/avo/releases/tag/v3.32.1
      Referenceadded
      —
      https://github.com/avo-hq/avo/security/advisories/GHSA-8fq9-273g-6mrg

      Source identifier: security-advisories@github.com

    One NVD translation into another language is hidden.

    Linked advisories

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