Unauthenticated code execution via HPACK path overflow
Published Sep 15, 2026 · Updated Sep 15, 2026
Out-of-bounds write in libwebsockets b4b5aed3903eaff09cd76a410f69bbe5dff66f8e allows remote attackers to execute code via HTTP/2. The lws_frag_append function in lib/roles/h2/hpack.c writes each decoded path byte to ah->data and increments ah->pos without first enforcing max_http_header_data. An unauthenticated network path to an HTTP/2 server using the affected library is required, and successful exploitation runs code in the server process context.
Summary
What happened
Out-of-bounds write in libwebsockets b4b5aed3903eaff09cd76a410f69bbe5dff66f8e allows remote attackers to execute code via HTTP/2. The lws_frag_append function in lib/roles/h2/hpack.c writes each decoded path byte to ah->data and increments ah->pos without first enforcing max_http_header_data. An unauthenticated network path to an HTTP/2 server using the affected library is required, and successful exploitation runs code in the server process context.
The record
- CVE
- CVE-2026-19773
- Published
- Sep 15, 2026
- Updated
- Sep 15, 2026
- Vendor
- libwebsockets
- Product
- libwebsockets
- Classifications
- T1190
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Sep 15, 2026CVE publishedPublication date reported by the CVE source.
- Sep 15, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
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- Affected versionversion=b4b5aed3903eaff09cd76a410f69bbe5dff66f8e
What conditions does exploitation require?
What is affected?
Published CVSS scores
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Attacks
What attackers are doing with it
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Weakness, pattern, technique
Public exploit references
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Technologies
Your stack
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Your stack
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