GO-2026-6612 BIT-golang-2026-78663 CVE-2026-78663
Double flow control refund on HTTP/2 server streams in net/http
- Severity
- 9.1 / 10
- Critical · CVSS 3.1
- Exploit chance (EPSS)
- 0.62%
- Chance of exploitation in the next 30 days. Higher than 49.82% of scored vulnerabilities.
- Known exploited
- No
- Not in CISA's catalog
- Weakness
- CWE-675 Multiple Operations on Resource in Single-Operation Context
- Fix
- Available
- 2 packages have a fixed version
Description
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.
Affected versions
Go
| Package | Vulnerable | Fixed in |
|---|---|---|
| golang.org/x/net | < 0.60.0 |
0.60.0 |
| stdlib | < 1.26.9 |
1.26.9 |
| stdlib | >= 1.27.0-0, < 1.27.2 |
1.27.2 |
How to fix
Move to the fixed version or later with your package manager, update the lockfile, and run your tests. If the package only arrives through another dependency, upgrade that dependency first. If none of its releases pulls a fixed version yet, force the version with your package manager's override.
golang.org/x/net Go → 0.60.0
- go
go get golang.org/x/net@v0.60.0 && go mod tidy
stdlib Go → 1.26.9
- go
go get stdlib@v1.26.9 && go mod tidy
Severity breakdown
CVSS 3.1 9.1
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H
- Attack vector
- Network
- Attack complexity
- Low
- Privileges required
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- None
- Integrity
- High
- Availability
- High
Weakness
CWE-675: Multiple Operations on Resource in Single-Operation Context
The product performs the same operation on a resource two or more times, when the operation should only be applied once.
References
Fixes and patches
Issue reports
Other links
Timeline
- Published
- Last updated by the source
- Latest EPSS score
Related advisories
| Advisory | Severity | Why it's related |
|---|---|---|
| GHSA-4374-p667-p6c8 HTTP/2 rapid reset can cause excessive work in net/http | High Known exploited | Also affects golang.org/x/net |
| GHSA-qppj-fm5r-hxr3 HTTP/2 Stream Cancellation Attack | Medium Known exploited | Also affects golang.org/x/net |
| CVE-2020-0601 Certificate validation bypass on Windows in crypto/x509 | High Known exploited | Also affects stdlib |
| GO-2026-6866 Check all ancestor namespace transitions when rendering raw text in html in golang.org/x/net | Not rated yet | Also affects golang.org/x/net |
| GO-2026-6860 Avoid quadratic complexity when coalescing text nodes in html in golang.org/x/net | Not rated yet | Also affects golang.org/x/net |
| RUSTSEC-2026-0382 Distrust compromised intermediate certificates in crypto/x509 | Medium | Also affects stdlib |
| GO-2026-6613 HTTP/1 server connection desynchronization after 2xx CONNECT response in net/http | High | Also affects stdlib |
| GO-2026-6609 Lack of limit on size of parsed Range headers in net/http | High | Also affects stdlib |
Credits: Ali Sherif (https://www.linkedin.com/in/ali-sherif-13812b276/)
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