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Vulnerability record · CVE-2021-29923 · published 7 August 2021

CVE-2021-29923: Golang go vulnerability

Golang · Go

Go before 1.17 does not properly consider extraneous zero characters at the beginning of an IP address octet, which (in some situations) allows attackers to bypass access control that is based on IP addresses, because of unexpected octal interpretation. This affects net.ParseIP and net.ParseCIDR.

7.5 CVSS 3.1 High EPSS 3.7% · top 10.7%
7.5CVSS 3.1 base score, v2 5.0
3.7%EPSS exploitation probability, 30 days
NoNot in CISA KEV
3Affected product versions listed by NVD
18References, 4 tagged exploit
17 Jun 2026Last modified by NVD

Description

Go before 1.17 does not properly consider extraneous zero characters at the beginning of an IP address octet, which (in some situations) allows attackers to bypass access control that is based on IP addresses, because of unexpected octal interpretation. This affects net.ParseIP and net.ParseCIDR.

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

Affected products

3 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
https://defcon.org/html/defcon-29/dc-29-speakers.html#kaoudis Third Party Advisory
https://github.com/golang/go/issues/30999 ExploitIssue TrackingThird Party Advisory
https://github.com/golang/go/issues/43389 Issue TrackingThird Party Advisory
https://github.com/sickcodes/security/blob/master/advisories/SICK-2021-016.md ExploitThird Party Advisory
https://go-review.googlesource.com/c/go/+/325829/ PatchThird Party Advisory
https://golang.org/pkg/net/#ParseCIDR Vendor Advisory
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/4CHKSFMHZVOBCZSSVRE3UEY
https://security.gentoo.org/glsa/202208-02 Third Party Advisory
https://www.oracle.com/security-alerts/cpujan2022.html PatchThird Party Advisory
https://defcon.org/html/defcon-29/dc-29-speakers.html#kaoudis Third Party Advisory
https://github.com/golang/go/issues/30999 ExploitIssue TrackingThird Party Advisory
https://github.com/golang/go/issues/43389 Issue TrackingThird Party Advisory
https://github.com/sickcodes/security/blob/master/advisories/SICK-2021-016.md ExploitThird Party Advisory
https://go-review.googlesource.com/c/go/+/325829/ PatchThird Party Advisory
https://golang.org/pkg/net/#ParseCIDR Vendor Advisory
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/4CHKSFMHZVOBCZSSVRE3UEY
https://security.gentoo.org/glsa/202208-02 Third Party Advisory
https://www.oracle.com/security-alerts/cpujan2022.html PatchThird Party Advisory

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Same products first, then exploited flaws of the same weakness class.

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Source: NIST National Vulnerability Database (record CVE-2021-29923), CISA KEV, FIRST EPSS (scores of 2026-09-26). This page is refreshed as NVD updates the record.