MediumCVE-2026-72722

    Discourse: Duplicate lookup reveals restricted topic titles through canonicalized URLs (CVE-2026-72722)

    Published Last modified Sources: CVE.org, OSV

    What is affected, what to do

    Discourse is an open-source discussion platform. Prior to 2026.1.6, 2026.5.2, 2026.6.1, and 2026.7.0, TopicLink.extract_from, TopicLink.ensure_entry_for, and TopicLink.duplicate_lookup do not consistently enforce Guardian.can_see? checks when processing internal links.

    Update Discourse to version 2026.1.6.

    Affected
    • Discourse gte 2026.5.0-latest, < 2026.5.2..*
    • Discourse lt *..2026.1.6
    Fixed in
    • Discourse 2026.1.6

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

    Metrics

    4.3

    Priority

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

    Source: Vendor (CNA), CVSS v3

    4.3

    CVSS v3

    Severity Medium on the scale from 0 to 10.

    Source: CVE.org, OSV

    0.4 %

    EPSS score

    Low — model estimates < 1% exploitation likelihood.

    Source: FIRST EPSS, percentile 38.2

    Show all metrics
    Severity
    Medium
    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
    56.16 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
    4.3 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
    4.3
    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
    38.2
    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
    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-862

    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
    Handle the vulnerability in regular vulnerability handling under Art. 21(2)(e) NIS2.
    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

    Discourse is an open-source discussion platform. Prior to 2026.1.6, 2026.5.2, 2026.6.1, and 2026.7.0, TopicLink.extract_from, TopicLink.ensure_entry_for, and TopicLink.duplicate_lookup do not consistently enforce Guardian.can_see? checks when processing internal links. An authenticated user can submit links to restricted topics, private messages, or hidden posts and receive canonicalized slugs or titles in the composer_messages duplicate_lookup response even though the targets are not visible to that user. This issue is fixed in versions 2026.1.6, 2026.5.2, 2026.6.1, and 2026.7.0.

    Source: NVD (NIST), OSV (Open Source Vulnerabilities), cvelistv5

    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
    discoursediscourse
    • ≥ 2026.5.0-latest, < 2026.5.2
    • < 2026.1.6
    • —
    • 2026.1.6
    Distribution and container packages (2)

    Downstream packages (e.g. Bitnami, Debian, Ubuntu, Red Hat). Versions refer to the distribution, not the vendor.

    Distribution and container packages
    Affected versionsFixed in
    bitnamidiscourse
    • 2026.5.0
    • 2026.6.0
    • —
    • —

    Vendors and products

    Weakness classes (CWE)

    • 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

    References & sources

    • github.comdiscourse/discourse/security/advisories/GHSA-4fx9-5m29-83p4x_refsource_CONFIRM
    • github.comdiscourse/discourse/pull/42091x_refsource_MISC
    • github.comdiscourse/discourse/pull/42092x_refsource_MISC
    • github.comdiscourse/discourse/pull/42093x_refsource_MISC
    • github.comdiscourse/discourse/pull/42094x_refsource_MISC
    • github.comdiscourse/discourse/commit/45abd925e46e8be40d2d047bced26628f26e…x_refsource_MISC
    • github.comdiscourse/discourse/commit/7d7ce546ac86e24a6512b321ace69fc52fe3…x_refsource_MISC
    • github.comdiscourse/discourse/commit/836a251d54a1004fb1c463a7d299b933b176…x_refsource_MISC
    • github.comdiscourse/discourse/commit/e54ba27eacee0f14f315e510e287e7ac2e4b…x_refsource_MISC
    • NVD (NIST)vuln/detail/CVE-2026-72722web

    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. ReceivedGitHub

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

      Weakness type: CWE-862

      Description added or changed

      Show 13 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Affected versions (publisher)added
      —
      discourse
      Descriptionadded
      —
      Discourse is an open-source discussion platform. Prior to 2026.1.6, 2026.5.2, 2026.6.1, and 2026.7.0, TopicLink.extract_from, TopicLink.ensure_entry_for, and TopicLink.duplicate_lookup do not consistently enforce Guardian.can_see? checks when processing internal links. An authenticated user can submit links to restricted topics, private messages, or hidden posts and receive canonicalized slugs or titles in the composer_messages duplicate_lookup response even though the targets are not visible to that user. This issue is fixed in versions 2026.1.6, 2026.5.2, 2026.6.1, and 2026.7.0.
      CVSSadded
      —
      AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N
      Weakness type (CWE)added
      —
      CWE-862
      Referenceadded
      —
      https://github.com/discourse/discourse/commit/45abd925e46e8be40d2d047bced26628f26e4e31
      Referenceadded
      —
      https://github.com/discourse/discourse/commit/7d7ce546ac86e24a6512b321ace69fc52fe37bf4
      Referenceadded
      —
      https://github.com/discourse/discourse/commit/836a251d54a1004fb1c463a7d299b933b176191f
      Referenceadded
      —
      https://github.com/discourse/discourse/commit/e54ba27eacee0f14f315e510e287e7ac2e4bdb1a
      Referenceadded
      —
      https://github.com/discourse/discourse/pull/42091
      Referenceadded
      —
      https://github.com/discourse/discourse/pull/42092
      Referenceadded
      —
      https://github.com/discourse/discourse/pull/42093
      Referenceadded
      —
      https://github.com/discourse/discourse/pull/42094
      Referenceadded
      —
      https://github.com/discourse/discourse/security/advisories/GHSA-4fx9-5m29-83p4

      Source identifier: security-advisories@github.com

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