CVE intelligence

CVE-2026-78659

Vulnerability intelligence

Published Oct 8, 2026Sources checked Oct 21, 2026

7.5HIGHCVSS out of 10

What this means

Review the available evidence

CVE-2026-78659 and is rated High severity with a CVSS score of 7.5. It is not in the current CISA KEV record we collected. That does not prove exploitation has not occurred.

What to do next

Remediation and response

Microsoft Security Response Center guidance

Vendor revision: Oct 21, 2026

Vendor remediation details

Release Notes

Vendor-listed releases

1.7.0-2
1.12.15-15
0.5.1-10
2.3.7-1
1.62.0-9
0.14.0-19
2.27.0-16
0.24.2-34
2.102.0-2
2.7.5-22
3.10.182-6
2.14.1-22
0.0.10-11
1.8.4-4
1.15.0-7
4.0.2-12
1.9.5-23
0.12.0-12
1.7.0-6
0.8.2-6
1.14.4-14
1.31.0-35
19.0.4-15

CISA KEVNot listedBased on the latest collected catalog

EPSS0.6%Estimated 30-day exploitation probability

Ransomware useNot markedCISA KEV ransomware field

Threat actors0Source-linked actor relationships

Overview

What is CVE-2026-78659?

When "Trailer" headers are sent by a client, the HTTP server internally uses the header values to populate the Request.Trailer map passed to the server handler. Because Request.Trailer is a map, each entry incurs memory overhead.

For HTTP/2 servers, a malicious client can exploit this by sending a "Trailer" header that declares a large number of fields, causing the server to allocate a disproportionate amount of memory while bypassing Server.MaxHeaderValueCount and Server.MaxHeaderBytes limits.

This exploit is not applicable for HTTP/1 servers, which do not support multiplexing a large number of requests over one TCP connection, and whose Server.MaxHeaderBytes are calculated differently.

Source: NVD