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GO-2026-4601 BIT-golang-2026-25679 CVE-2026-25679

Incorrect parsing of IPv6 host literals in net/url

High Go
Severity
7.5 / 10
High · CVSS 3.1
Exploit chance (EPSS)
0.83%
Chance of exploitation in the next 30 days. Higher than 57.49% of scored vulnerabilities.
Known exploited
No
Not in CISA's catalog
Weakness
CWE-1286 Improper Validation of Syntactic Correctness of Input
CWE-425 Direct Request ('Forced Browsing')
Fix
1.26.1
Upgrade stdlib to this version or later

Description

url.Parse insufficiently validated the host/authority component and accepted some invalid URLs.

Affected versions

Go

PackageVulnerableFixed in
stdlib
< 1.25.8
>= 1.26.0-0, < 1.26.1
1.25.8
1.26.1

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 → 1.26.1

go
go get stdlib@v1.26.1 && 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-1286: Improper Validation of Syntactic Correctness of Input

The product receives input that is expected to be well-formed - i.e., to comply with a certain syntax - but it does not validate or incorrectly validates that the input complies with the syntax.

How to prevent it
  • Implementation: Assume all input is malicious. Use an "accept known good" input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does. When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules. As an example of business rule logic, "boat" may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as "red" or "blue." Do not rely exclusively on looking for malicious or malformed inputs. This is likely to miss at least one undesirable input, especially if the code's environment changes. This can give attackers enough room to bypass the intended validation. However, denylists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright.

CWE-425: Direct Request ('Forced Browsing')

The web application does not adequately enforce appropriate authorization on all restricted URLs, scripts, or files.

How to prevent it
  • Architecture and Design, Operation: Apply appropriate access control authorizations for each access to all restricted URLs, scripts or files.
  • Architecture and Design: Consider using MVC based frameworks such as Struts.

References

Advisories

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
HTTP/2 rapid reset can cause excessive work in net/http
High Known exploited Also affects stdlib
CVE-2020-0601
Certificate validation bypass on Windows in crypto/x509
High Known exploited Also affects stdlib
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-2026-6607
Reject malformed ECH outer extension references in crypto/tls
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

Credits: Masaki Hara (https://github.com/qnighy) of Wantedly

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