CVE-2026-78663Network attack vectorHinoki check available

Buffer-limit bypass via duplicate flow-control refunds

Published Oct 8, 2026 · Updated Oct 8, 2026

HTTP/2 flow-control accounting in Go net/http allows remote attackers to exceed connection buffering limits via stream resets. The server refunds sent-but-unread data when a stream resets, then refunds the same data again when a request handler reads it. Exploitation requires an HTTP/2 server and that read sequence; buffering remains bounded by concurrent-stream and stream-level limits, and no specific crash or hang is documented.

CVSS severityUnavailable
Unscored
EPSS probability0.57%
Next 30 days · Oct 19, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkAvailable
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Summary

What happened

HTTP/2 flow-control accounting in Go net/http allows remote attackers to exceed connection buffering limits via stream resets. The server refunds sent-but-unread data when a stream resets, then refunds the same data again when a request handler reads it. Exploitation requires an HTTP/2 server and that read sequence; buffering remains bounded by concurrent-stream and stream-level limits, and no specific crash or hang is documented.

The record

CVE
CVE-2026-78663
Published
Oct 8, 2026
Updated
Oct 8, 2026
Vendor
Go standard library
Product
net/http
Classifications
CWE-675, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Oct 8, 2026CVE publishedPublication date reported by the CVE source.
  2. Oct 8, 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?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=0 <1.26.9

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Go standard library · net/httpversion=0 <1.26.9
golang.org/x/net · golang.org/x/net/http2version=0 <0.60.0
Go standard library · net/http/internal/http2version=1.27.0-0 <1.27.2

Published CVSS scores

No CVSS assessment is available in this record.

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Activity data is delayed. The latest report is Sep 28, 2026.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 22, 2026Sep 28, 2026
Latest reporting daySep 28, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-675Multiple Operations on Resource in Single-Operation Context
T1499.004Exploitation for Service Exhaustion

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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