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GO-2026-6607 BIT-golang-2026-97031 CVE-2026-97031

Reject malformed ECH outer extension references in crypto/tls

High Go
Severity
7.5 / 10
High · CVSS 3.1
Exploit chance (EPSS)
0.52%
Chance of exploitation in the next 30 days. Higher than 44.09% of scored vulnerabilities.
Known exploited
No
Not in CISA's catalog
Weakness
CWE-405 Asymmetric Resource Consumption (Amplification)
Fix
1.27.2
Upgrade stdlib to this version or later

Description

Multiple ECH outer extension references are not permitted under RFC 9849; previously, a client could send a well-crafted packet that could trigger memory exhaustion in the server process by specifying multiple references.

We now reject these as malformed and curb the memory amplification vector as a result.

Affected versions

Go

PackageVulnerableFixed in
stdlib
< 1.26.9
>= 1.27.0-0, < 1.27.2
1.26.9
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.

stdlib Go → 1.27.2

go
go get stdlib@v1.27.2 && go mod tidy

Severity breakdown

CVSS 3.1 7.5

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

Weakness

CWE-405: Asymmetric Resource Consumption (Amplification)

The product does not properly control situations in which an adversary can cause the product to consume or produce excessive resources without requiring the adversary to invest equivalent work or otherwise prove authorization, i.e., the adversary's influence is "asymmetric."

How to prevent it
  • Architecture and Design: An application must make resources available to a client commensurate with the client's access level.
  • Architecture and Design: An application must, at all times, keep track of allocated resources and meter their usage appropriately.
  • System Configuration: Consider disabling resource-intensive algorithms on the server side, such as Diffie-Hellman key exchange.

References

Fixes and patches

Issue reports

Other links

Timeline

  1. Published
  2. Last updated by the source
  3. Latest EPSS score
AdvisorySeverityWhy it's related
GHSA-4374-p667-p6c8
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CVE-2020-0601
Certificate validation bypass on Windows in crypto/x509
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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
GO-2026-6608
Memory limit bypass when parsing MIME headers in net/textproto, mime/multipart
High Also affects stdlib
GO-2026-6604
Root.Mkdir(All) can follow junctions out of the root on Windows in os
Critical Also affects stdlib
GO-2026-6600
Recognize yield as regexp preceder keyword in html/template
Medium Also affects stdlib
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