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Vulnerabilities

Vulnerability · CVE-2026-78663

Double flow control refund on HTTP/2 server streams in net/http

Published Oct 8, 2026 · catalog updated Oct 16, 2026 · Double flow control refund

Check if you run it

No confirmed exploitation is on record for CVE-2026-78663. EPSS is 0.57%. Act only if a listed version of Double flow control refund is installed.

Gaps on this record

  • The stored product name is a package slug. The name on this page is taken from the title (Double flow control refund).
  • No vendor fix or required action is stored. Compare the linked advisory before you change production.
Severity
Unknown—
Known exploitation
Not in CISA/VulnCheck KEV
EPSS
0.57%
Remediation
Not established
Affected products
Go golang.org/x/net · Go stdlib

The HTTP/2 server can refund connection-level flow control twice for the same data: Once when a client resets a stream (refunding data for any sent-but-unread portion of the stream), and again when a request handler reads the buffered data. A malicious client can exploit this to bypass the configured connection-level flow control limit (MaxReceiveBufferPerConnection). Total buffered data is still limited by the concurrent stream limit and stream-level flow control.

Are you affected?

Enter the version you run. The result uses only the ranges stored on this record.

The check returns affected, not affected, or incomplete. It does not guess a version that is missing from the record.

  • Go golang.org/x/net0 → 0.60.0
  • Go stdlib0 → 1.26.9
  • Go stdlib1.27.0-0 → 1.27.2

How to fix CVE-2026-78663

What to do

Three questions, each answered from this record only. Confirm the vendor advisory before you patch.

Should you patch?

No confirmed exploitation is on record for CVE-2026-78663. EPSS is 0.57%. Act only if a listed version of Double flow control refund is installed.

Which versions are affected?

Compare what you have installed with 0 → 0.60.0, 0 → 1.26.9, 1.27.0-0 → 1.27.2. Compare the installed version with the linked vendor advisory before you change production.

What should an analyst verify?

No weakness class is stored. EPSS 0.57%. There is no CISA KEV listing. No Exploit-DB or Metasploit reference is linked. Use the source links for the original advisory.

Code

The project this record applies to. Exploit listings stay in References.

No public source repository is identified for this product.

Timeline

Detection, updates, and resolution for this record.

  1. Oct 8, 2026 · OpenSSF OSV / OSV Scanner

    Detected

    The HTTP/2 server can refund connection-level flow control twice for the same data: Once when a client resets a stream (refunding data for any sent-but-unread portion of the stream), and again when a request handler reads the buffered data. A malicious client can exploit this to bypass the configured connection-level flow control limit (MaxReceiveBufferPerConnection). Total buffered data is still

  2. Oct 16, 2026 · OpenSSF OSV / OSV Scanner

    Fix available

    stdlib fixed in 1.26.9; stdlib fixed in 1.27.2; golang.org/x/net fixed in 0.60.0

  3. Oct 16, 2026 · OpenSSF OSV / OSV Scanner

    Fix available

    stdlib fixed in 1.26.9

  4. Oct 16, 2026 · OpenSSF OSV / OSV Scanner

    Fix available

    stdlib fixed in 1.27.2

  5. Oct 16, 2026 · OpenSSF OSV / OSV Scanner

    Fix available

    golang.org/x/net fixed in 0.60.0

  6. Oct 16, 2026 · OpenSSF OSV / OSV Scanner

    Updated

    The HTTP/2 server can refund connection-level flow control twice for the same data: Once when a client resets a stream (refunding data for any sent-but-unread portion of the stream), and again when a request handler reads the buffered data. A malicious client can exploit this to bypass the configured connection-level flow control limit (MaxReceiveBufferPerConnection). Total buffered data is still

Sources

References

Freshness

Last verified in this catalog Oct 18, 2026. Significant claims (KEV, EPSS, CVSS, affected ranges) come from the source rows above — open the original publisher for the authoritative advisory.