major vulnerability· requires attention

Unauthenticated RCE in libwebsockets (widely embedded websocket/HTTP libraries) with CVSS 9.8 — broad impact on apps, servers and IoT devices.

Web

CVE-2026-19773

9.8

Critical

EPSS 0.65%Patch available

Unauthenticated HTTP/2 HPACK parsing RCE in libwebsockets (CVE-2026-19773)

exploited

No known exploitation not in CISA KEV as of our last sync

fix

Patch available see the advisory in the references

likelihood

EPSS 0.65%top 50% of scored CVEs

Published 15 Sept 2026Analysed here 18 Sept 2026CVSS scored by the publisher (CNA)

common questions

Is CVE-2026-19773 being exploited?

Not confirmed. CVE-2026-19773 does not appear in CISA's Known Exploited Vulnerabilities catalog, which records only exploitation that has been observed and reported publicly. That is evidence of absence of a report, not evidence the flaw is unattacked. EPSS currently estimates a 0.65% probability of exploitation in the next 30 days.

How severe is CVE-2026-19773?

CVE-2026-19773 is rated Critical with a CVSS score of 9.8. Severity describes how bad exploitation would be, not how likely it is: pair it with exploitation evidence before deciding what to patch first.

Is there a patch for CVE-2026-19773?

Yes. A fix has been recorded for CVE-2026-19773. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.

What does CVE-2026-19773 affect?

CVE-2026-19773 affects libwebsockets, Applications linking libwebsockets, Servers exposing HTTP/2 via libwebsockets, Embedded/IoT devices using libwebsockets. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.

What should I do about CVE-2026-19773?

Upgrade to the patched libwebsockets release or apply the upstream commit; if not possible, disable HTTP/2 and restrict access.

Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.

executive summary

technical analysis

affected

libwebsocketsApplications linking libwebsocketsServers exposing HTTP/2 via libwebsocketsEmbedded/IoT devices using libwebsockets

impact

Remote unauthenticated out‑of‑bounds write in HTTP/2 HPACK path parsing enabling arbitrary code execution in the process.

action required

Immediate action required

affected versions

libwebsockets

affectedb4b5aed3903eaff09cd76a410f69bbe5dff66f8e

As published in the CVE Program record. A version outside these ranges is not a statement that it is unaffected — vendors sometimes understate a range, and distribution-backported builds carry upstream numbers that do not reflect what was patched into them.

cisa ssvc

exploitation: none
automatable: yes
technical impact: total

Assessed by CISA 15 Sept 2026 (SSVC 2.0.3).

timeline

15 Sept 2026CISA SSVC assessment: exploitation none
15 Sept 2026Published · 1 day later
16 Sept 2026CVE record last updated · same day later
18 Sept 2026Analysed by vulneraibility.com · 3 days later

how to fix

Remediation steps are tailored for users whose stack is affected. Add this technology to your stack to see the fix checklist.

references

NVD CVE.org CVE Details Source

2 references in the CVE record: 2 advisories

Advisoryzerodayinitiative.com /advisories/ZDI-26-590/
Advisorygithub.com /warmcat/libwebsockets/commit/824151862f37bc72f46d9a3e01d5b9408d313a0b

sources

CVE List (CVE.org): description, affected versions, references; CVE Terms of Use
NVD: CVSS and CPE data
CISA Vulnrichment (ADP): SSVC decision points
FIRST EPSS: exploit probability and percentile
Summary, impact and triage tags: written by our AI analysis pipeline from the sources above. Check them against the sources.

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