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CVE-2026-42270 Countly CVE debrief

CVE-2026-42270 is a high-severity vulnerability in countly-server, a product analytics solution. An unauthenticated request can cause a Denial of Service (DoS) via an unhandled stream exception, allowing repeated requests to keep the analytics API unavailable. The issue is fixed in versions 24.05.50 and 25.03.44. This vulnerability affects the product's ability to handle stream exceptions properly, leading to potential service unavailability. Defenders should assess exposure and apply patches to prevent potential DoS attacks. The vulnerability can be exploited by sending a URL-encoded dot in a request, which can make createReadStream open a directory, emit an asynchronous EISDIR  

Vendor
Countly
Product
countly-server
CVSS
HIGH 7.5
CISA KEV
Not listed in stored evidence
Original CVE published
2026-10-16
Original CVE updated
2026-10-16
Advisory published
2026-10-16
Advisory updated
2026-10-16

Who should care

Defenders responsible for countly-server installations should assess exposure and apply patches to prevent potential DoS attacks. This includes verifying the installed countly-server version and updating to a fixed version if necessary. Additionally, defenders should monitor analytics API availability and investigate potential DoS attacks. Security teams and vulnerability management teams should also be aware of the potential impact of this vulnerability  

Why it matters

CVE-2026-42270 is a high-severity vulnerability in countly-server that allows unauthenticated Denial of Service (DoS) attacks. Defenders should verify exposure and apply patches to prevent potential service unavailability.

  • Potential Denial of Service (DoS) attacks against analytics API
  • Unauthenticated requests can cause service unavailability
  • Requires verification of exposure and patch application

Technical summary

The countly-server product analytics solution has a vulnerability that allows an unauthenticated request to cause a Denial of Service (DoS) via an unhandled stream exception. This can be exploited by sending a URL-encoded dot in a request, which can make createReadStream open a directory, emit an asynchronous EISDIR error, and terminate the Node.js process. The issue is fixed in versions 24.05.50 and 25.03.44. Defenders should prioritize verifying exposure and applying patches to prevent potential DoS attacks. The vulnerability affects  

Defensive priority

Defenders should prioritize verifying exposure and applying patches to prevent potential DoS attacks.

Recommended defensive actions

  • Verify exposure by checking if the installed countly-server version is prior to 24.05.50 or 25.03.44.
  • Apply patches by updating to version 24.05.50 or 25.03.44.
  • Monitor analytics API availability and investigate potential DoS attacks.
  • Review compensating controls for exposed systems while remediation is scheduled and verified.
  • Check relevant monitoring, detection, and logs for exposed assets that need extra review.
  • Track exceptions, retest remediated assets, and close the item only after evidence is documented.
  • Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up.

Evidence notes

The CVE record and source item provide details on the vulnerability, affected versions, and fixed versions. The vulnerability allows an unauthenticated request to cause a Denial of Service (DoS) via an unhandled stream exception. The issue is fixed in versions 24.05.50 and 25.03.44. Defenders should verify exposure and apply patches to prevent potential service unavailability. The CVE record was published on 2026-10-16T16:02:00.196Z and has not been modified since then. The source item provides additional information on the  

Sources and references

Verified primary and authoritative sources

  • CVE-2026-42270 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2026-42270

    CVE Program - Official CVE Program record with source-provided CVE metadata.

  • CVE-2026-42270 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2026-42270

    NIST National Vulnerability Database - Official NIST NVD detail page and source-specific vulnerability assessment.

Supplemental references

  • countly-server: Unauthenticated Denial of Service (DoS) via Unhandled Stream Exception

    Unverified legacy reference

    URL: https://raw.githubusercontent.com/CVEProject/cvelistV5/main/cves/2026/42xxx/CVE-2026-42270.json

    cve_program_cvelist_v5

  • Source reference

    Unverified legacy reference

    URL: https://github.com/Countly/countly-server/security/advisories/GHSA-86cv-qwp9-jwp3

    Supplemental source - x_refsource_CONFIRM

  • Source reference

    Unverified legacy reference

    URL: https://github.com/Countly/countly-server/commit/72f19bc5161117fa02a224bf9f7316bf42dae58d

    Supplemental source - x_refsource_MISC

  • Source reference

    Unverified legacy reference

    URL: https://github.com/Countly/countly-server/commit/f9ad31480f94ee3ccc0f12708c8804be9c803f95

    Supplemental source - x_refsource_MISC

  • Source reference

    Unverified legacy reference

    URL: https://github.com/Countly/countly-server/releases/tag/24.05.50

    Supplemental source - x_refsource_MISC

  • Source reference

    Unverified legacy reference

    URL: https://github.com/Countly/countly-server/releases/tag/25.03.44

    Supplemental source - x_refsource_MISC

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.