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CVE-2026-19773

libwebsockets HTTP/2 HPACK Path Header Parsing Out-Of-Bounds Write Remote Code Execution Vulnerability

9.8 CriticalFix available

libwebsockets HTTP/2 HPACK Path Header Parsing Out-Of-Bounds Write Remote Code Execution Vulnerability. This vulnerability allows remote attackers to execute arbitrary code on affected installations of libwebsockets. Authentication is not required to exploit this vulnerability.

The specific flaw exists within the parsing of HTTP/2 HPACK path header. The issue results from the lack of proper validation of user-supplied data, which can result in a write past the end of an allocated buffer. An attacker can leverage this vulnerability to execute code in the context of the current process. Was ZDI-CAN-31036.

Attack profile

How easy it is to exploit

Attack vector
Network
Complexity
Low
Privileges needed
None
User interaction
None

What an attacker can affect

Confidentiality
High
Integrity
High
Availability
High

Exploit likelihood

0.65%Unchanged since Sep 16, 2026
90%50%10%1%

What each source reports

CVE List Score used 9.8

libwebsockets HTTP/2 HPACK Path Header Parsing Out-Of-Bounds Write Remote Code Execution Vulnerability

libwebsockets HTTP/2 HPACK Path Header Parsing Out-Of-Bounds Write Remote Code Execution Vulnerability. This vulnerability allows remote attackers to execute arbitrary code on affected installations of libwebsockets. Authentication is not required to exploit this vulnerability.

The specific flaw exists within the parsing of HTTP/2 HPACK path header. The issue results from the lack of proper validation of user-supplied data, which can result in a write past the end of an allocated buffer. An attacker can leverage this vulnerability to execute code in the context of the current process. Was ZDI-CAN-31036.

Record
CVE-2026-19773
CVSS 3.0
9.8 CriticalCVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Weakness
CWE-787
Updated
2026-11-02
EUVDEUVD-2026-79130 9.8

libwebsockets HTTP/2 HPACK Path Header Parsing Out-Of-Bounds Write Remote Code Execution Vulnerability. This vulnerability allows remote attackers to execute arbitrary code on affected installations of libwebsockets. Authentication is not required to exploit this vulnerability.

The specific flaw exists within the parsing of HTTP/2 HPACK path header. The issue results from the lack of proper validation of user-supplied data, which can result in a write past the end of an allocated buffer. An attacker can leverage this vulnerability to execute code in the context of the current process. Was ZDI-CAN-31036.

Record
EUVD-2026-79130
CVSS 3.0
9.8 CriticalCVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Updated
2026-11-02
GitHub AdvisoriesGHSA-r4m8-276f-3r2f 9.8

libwebsockets HTTP/2 HPACK Path Header Parsing Out-Of-Bounds Write Remote Code Execution...

libwebsockets HTTP/2 HPACK Path Header Parsing Out-Of-Bounds Write Remote Code Execution Vulnerability. This vulnerability allows remote attackers to execute arbitrary code on affected installations of libwebsockets. Authentication is not required to exploit this vulnerability.

The specific flaw exists within the parsing of HTTP/2 HPACK path header. The issue results from the lack of proper validation of user-supplied data, which can result in a write past the end of an allocated buffer. An attacker can leverage this vulnerability to execute code in the context of the current process. Was ZDI-CAN-31036.

Record
GHSA-r4m8-276f-3r2f
CVSS 3.0
9.8 CriticalCVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Weakness
CWE-787
Updated
2026-11-02
NVD 9.8

libwebsockets HTTP/2 HPACK Path Header Parsing Out-Of-Bounds Write Remote Code Execution Vulnerability. This vulnerability allows remote attackers to execute arbitrary code on affected installations of libwebsockets. Authentication is not required to exploit this vulnerability.

The specific flaw exists within the parsing of HTTP/2 HPACK path header. The issue results from the lack of proper validation of user-supplied data, which can result in a write past the end of an allocated buffer. An attacker can leverage this vulnerability to execute code in the context of the current process. Was ZDI-CAN-31036.

Record
CVE-2026-19773
CVSS 3.0
9.8 CriticalCVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Weakness
CWE-787
Updated
2026-11-02
OSV 9.8

libwebsockets HTTP/2 HPACK Path Header Parsing Out-Of-Bounds Write Remote Code Execution Vulnerability

libwebsockets HTTP/2 HPACK Path Header Parsing Out-Of-Bounds Write Remote Code Execution Vulnerability. This vulnerability allows remote attackers to execute arbitrary code on affected installations of libwebsockets. Authentication is not required to exploit this vulnerability.

The specific flaw exists within the parsing of HTTP/2 HPACK path header. The issue results from the lack of proper validation of user-supplied data, which can result in a write past the end of an allocated buffer. An attacker can leverage this vulnerability to execute code in the context of the current process. Was ZDI-CAN-31036.

Record
CVE-2026-19773
CVSS 3.0
9.8 CriticalCVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Weakness
CWE-787
Updated
2026-11-02
OSVDEBIAN-CVE-2026-19773 9.8

libwebsockets HTTP/2 HPACK Path Header Parsing Out-Of-Bounds Write Remote Code Execution Vulnerability. This vulnerability allows remote attackers to execute arbitrary code on affected installations of libwebsockets. Authentication is not required to exploit this vulnerability. The specific flaw exists within the parsing of HTTP/2 HPACK path header. The issue results from the lack of proper validation of user-supplied data, which can result in a write past the end of an allocated buffer. An attacker can leverage this vulnerability to execute code in the context of the current process. Was ZDI-CAN-31036.

Record
DEBIAN-CVE-2026-19773
CVSS 3.0
9.8 CriticalCVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Updated
2026-11-02
OSVOESA-2026-4076 7.3

libwebsockets security update

Libwebsockets (LWS) is a flexible, lightweight pure C library for implementing modern network protocols easily with a tiny footprint, using a nonblocking event loop.

Security Fix(es):

libwebsockets HTTP/2 HPACK Path Header Parsing Out-Of-Bounds Write Remote Code Execution Vulnerability. This vulnerability allows remote attackers to execute arbitrary code on affected installations of libwebsockets. Authentication is not required to exploit this vulnerability.

The specific flaw exists within the parsing of HTTP/2 HPACK path header. The issue results from the lack of proper validation of user-supplied data, which can result in a write past the end of an allocated buffer. An attacker can leverage this vulnerability to execute code in the context of the current process. Was ZDI-CAN-31036.(CVE-2026-19773)

A vulnerability classified as critical was found in warmcat libwebsockets 4.5.0. The vulnerability is in the function report_raw_cbor in lib/misc/lecp.c when handling LECP CBOR recordings. This issue allows an out-of-bounds write (CWE-787), which could affect confidentiality, integrity, and availability. A proof-of-concept exploit is available.(CVE-2026-78161)

Record
OESA-2026-4076
CVSS 3.1
7.3 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L
Updated
2026-11-02
OSVUBUNTU-CVE-2026-19773 9.8

libwebsockets HTTP/2 HPACK Path Header Parsing Out-Of-Bounds Write Remote Code Execution Vulnerability. This vulnerability allows remote attackers to execute arbitrary code on affected installations of libwebsockets. Authentication is not required to exploit this vulnerability. The specific flaw exists within the parsing of HTTP/2 HPACK path header. The issue results from the lack of proper validation of user-supplied data, which can result in a write past the end of an allocated buffer. An attacker can leverage this vulnerability to execute code in the context of the current process. Was ZDI-CAN-31036.

Record
UBUNTU-CVE-2026-19773
CVSS 3.0
9.8 CriticalCVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Updated
2026-11-02
OSVUSN-8893-1 No score

libwebsockets vulnerabilities

It was discovered that libwebsockets did not properly validate user-supplied data when parsing HTTP/2 HPACK path headers, which could result in a write past the end of an allocated buffer. An attacker could possibly use this issue to execute arbitrary code. (CVE-2026-19773)

It was discovered that libwebsockets did not properly handle CBOR recording in the LECP parser, which could result in a write past the end of an allocated buffer. An attacker could possibly use this issue to cause a crash or execute arbitrary code. (CVE-2026-78161)

Record
USN-8893-1
Updated
2026-11-02

Affected products

Affected packages

Affected packages
PackageAffectedFixed
libwebsockets
Debian:12
All versions, plus listed versions
4.1.6-34.1.6-3.14.3.2-14.3.2-24.3.2-3
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4.3.2-44.3.3-14.3.3-1.14.3.3-1.1~exp14.3.5-14.3.5-24.3.5-34.3.5-44.3.5-4.14.3.5-54.3.5-64.3.5-7
None known
libwebsockets
Debian:13
before 4.3.5-1+deb13u3, plus listed versions
4.3.5-14.3.5-1+deb13u14.3.5-1+deb13u2
4.3.5-1+deb13u3
libwebsockets
Debian:14
before 4.3.5-7, plus listed versions
4.3.5-14.3.5-24.3.5-34.3.5-44.3.5-4.14.3.5-54.3.5-6
4.3.5-7
libwebsockets
openEuler:24.03-LTS-SP1
before 4.3.3-8.oe2403sp1
4.3.3-8.oe2403sp1
libwebsockets
openEuler:24.03-LTS-SP3
before 4.3.3-8.oe2403sp3
4.3.3-8.oe2403sp3
libwebsockets
openEuler:24.03-LTS-SP4
before 4.3.3-8.oe2403sp4
4.3.3-8.oe2403sp4
libwebsockets
openEuler:20.03-LTS-SP4
before 4.3.0-11.oe2003sp4
4.3.0-11.oe2003sp4
libwebsockets
openEuler:22.03-LTS-SP4
before 4.3.0-11.oe2203sp4
4.3.0-11.oe2203sp4
libwebsockets
Ubuntu:Pro:16.04:LTS
before 1.7.1-1ubuntu0.1~esm1, plus listed versions
1.2.2-11.6.0-31.6.0-41.6.0-51.6.1-11.7.0-1ubuntu11.7.0-21.7.1-1
1.7.1-1ubuntu0.1~esm1
libwebsockets
Ubuntu:Pro:18.04:LTS
before 2.0.3-3ubuntu0.1~esm1, plus listed versions
2.0.3-32.0.3-3build1
2.0.3-3ubuntu0.1~esm1
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Affected packages
PackageAffectedFixed
libwebsockets
Ubuntu:Pro:20.04:LTS
before 3.2.1-3ubuntu0.1~esm3, plus listed versions
2.0.3-3build13.2.1-33.2.1-3ubuntu0.1~esm13.2.1-3ubuntu0.1~esm2
3.2.1-3ubuntu0.1~esm3
libwebsockets
Ubuntu:Pro:22.04:LTS
before 4.0.20-2ubuntu1.1+esm2, plus listed versions
4.0.20-24.0.20-2ubuntu14.0.20-2ubuntu1.14.0.20-2ubuntu1.1+esm1
4.0.20-2ubuntu1.1+esm2
libwebsockets
Ubuntu:Pro:24.04:LTS
before 4.3.3-1.1ubuntu0.1~esm3, plus listed versions
4.3.2-44.3.3-14.3.3-1.1build14.3.3-1.1build24.3.3-1.1build34.3.3-1.1ubuntu0.1~esm14.3.3-1.1ubuntu0.1~esm2
4.3.3-1.1ubuntu0.1~esm3
libwebsockets
Ubuntu:Pro:26.04:LTS
before 4.3.5-3ubuntu1.2+esm1, plus listed versions
4.3.5-14.3.5-34.3.5-3ubuntu14.3.5-3ubuntu1.1
4.3.5-3ubuntu1.2+esm1

History

History
RecordedChangedSources
first indexedCVE List, EUVD, GitHub Advisories, NVD, OSV

Dates are when Every CVE recorded each change. Upstream dates may differ.

In short

CVE-2026-19773 is a critical vulnerability (CVSS 9.8) in Libwebsockets, published September 15, 2026. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 0.65%, the 51st percentile. Fixed in libwebsockets 4.3.5-1+deb13u3.

References

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