HighCVE-2026-93748

    http-cache-semantics through 4.2.0 Cross-User Cache Disclosure via max-stale (CVE-2026-93748)

    Published Last modified Sources: Red Hat, CVE.org, OSV, Msrc Update Guide, BSI

    What is affected, what to do

    A flaw was found in http-cache-semantics. This vulnerability allows unauthenticated attackers to retrieve cached responses, including sensitive session credentials like Set-Cookie values, belonging to other users.

    The available sources name no fixed version. Check the vendor guidance in the references below.

    Affected
    • Kornelski Http-cache-semantics lte *..4.2.0

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

    Metrics

    8.7

    Priority

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

    Source: Vendor (CNA), CVSS v4

    7.5

    CVSS v3

    Severity High on the scale from 0 to 10.

    Source: Red Hat, CVE.org, OSV, Msrc Update Guide, BSI

    0.6 %

    EPSS score

    Low — model estimates < 1% exploitation likelihood.

    Source: FIRST EPSS, percentile 47.1

    Show all metrics
    Severity
    High
    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
    88.86 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
    8.7 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
    7.5
    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
    8.7
    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
    47.1
    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: none known · automatable · Technical impact: partial
    Source: CISA Vulnrichment, as of 14 October 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-524

    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

    A flaw was found in http-cache-semantics. This vulnerability allows unauthenticated attackers to retrieve cached responses, including sensitive session credentials like Set-Cookie values, belonging to other users. This occurs because the component fails to properly validate security-zeroed cache entries when processing client `max-stale` directives. By requesting the same URL with a large `max-stale` value, an attacker can obtain another user's session credentials from shared-cache entries that were intended to be secure.

    Source: redhat_csaf, cvelistv5, NVD (NIST), OSV (Open Source Vulnerabilities), Microsoft Security Update Guide, BSI WID Portal, BSI CSAF

    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
    kornelskihttp-cache-semantics
    • ≤ 4.2.0
    • —
    npmhttp-cache-semantics
    • —
    • —

    Weakness classes (CWE)

    • CWE-524Use of Cache Containing Sensitive Information

      Base

      The code uses a cache that contains sensitive information, but the cache can be read by an actor outside of the intended control sphere.

      Entry at MITRE CWE-524

    References & sources

    • github.comGitHub Issue #56Issue tracking, web
    • github.comkornelski/http-cache-semanticsProduct, package
    • github.commax-stale stale-serving branch that re-serves a zero-lifetime entryTechnical description, web
    • github.commaxAge() zeroing for shared Set-Cookie and proxy-revalidate responsesTechnical description, web
    • vulncheck.comVulnCheck Advisory: http-cache-semantics through 4.2.0 Cross-User Cache Disclosure via max-staleThird-party advisory, web
    • NVD (NIST)vuln/detail/CVE-2026-93748advisory
    • github.comkornelski/http-cache-semantics/issues/56web

    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: none known, automatable: yes

      Show 3 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Referenceremoved
      https://github.com/kornelski/http-cache-semantics/issues/56
      —
      SSVC assessmentremoved
      {"id":"CVE-2026-93748","role":"CISA Coordinator","options":[{"exploitation":"poc"},{"automatable":"yes"},{"technicalImpact":"partial"}],"version":"2.0.3","timestamp":"2026-09-18T20:05:06.835112Z"}
      —
      SSVC assessmentadded
      —
      {"id":"CVE-2026-93748","role":"CISA Coordinator","options":[{"exploitation":"none"},{"automatable":"yes"},{"technicalImpact":"partial"}],"version":"2.0.3","timestamp":"2026-10-14T22:56:33.212079Z"}

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

    2. Record modifiedCVE Program

      Show the original change
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Referenceadded
      —
      https://github.com/kornelski/http-cache-semantics/issues/56#issuecomment-5975759591

      Source identifier: af854a3a-2127-422b-91ae-364da2661108

    3. Record modifiedCISA ADP

      CISA assessment (SSVC): exploitation: proof of concept, automatable: yes

      Show 2 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Referenceadded
      —
      https://github.com/kornelski/http-cache-semantics/issues/56
      SSVC assessmentadded
      —
      {"id":"CVE-2026-93748","role":"CISA Coordinator","options":[{"exploitation":"poc"},{"automatable":"yes"},{"technicalImpact":"partial"}],"version":"2.0.3","timestamp":"2026-09-18T20:05:06.835112Z"}

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

    4. ReceivedVulnCheck

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

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

      Weakness type: CWE-524

      Description added or changed

      Show 10 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Descriptionadded
      —
      http-cache-semantics through 4.2.0 fails to properly validate security-zeroed cache entries when processing client max-stale directives, allowing unauthenticated attackers to retrieve cached responses belonging to other users. Attackers can request the same URL with a large max-stale value to obtain another user's Set-Cookie session credentials from shared-cache entries that were deliberately zeroed for security reasons.
      CVSSadded
      —
      AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/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
      CVSSadded
      —
      AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
      Weakness type (CWE)added
      —
      CWE-524
      Affected versions (publisher)added
      —
      New affected value received. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/93xxx/CVE-2026-93748.json">CVE-2026-93748</a>
      Referenceadded
      —
      https://github.com/kornelski/http-cache-semantics
      Referenceadded
      —
      https://github.com/kornelski/http-cache-semantics/blob/f01112e954b83cfa8765b633ba880e5e980aa54c/index.js#L425-L441
      Referenceadded
      —
      https://github.com/kornelski/http-cache-semantics/blob/f01112e954b83cfa8765b633ba880e5e980aa54c/index.js#L603-L623
      Referenceadded
      —
      https://github.com/kornelski/http-cache-semantics/issues/56
      Referenceadded
      —
      https://www.vulncheck.com/advisories/http-cache-semantics-through-4.2.0-cross-user-cache-disclosure-via-max-stale

      Source identifier: disclosure@vulncheck.com

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