CVE-2026-27145: Go standard library crypto/x509 · Inefficient Algorithmic Complexity
Affects Go standard library crypto/x509Source CVE Database V5
Not known to be exploited · CVSS 6.5 Medium : upgrade to 1.26.4 or 1.25.11 when convenient.
Data as of 5 Nov 2026, 00:01 UTC
- EPSS
- 0.5% chance of exploitation in 30 days – higher than 48% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
- CISA SSVC
- Exploitation
- No evidence of active exploitation and no public proof of concept
- Automatable
- Attackers cannot reliably automate steps 1–4 of the kill chain
- Technical impact
- Limited control over the software or limited information exposure
CISA SSVC assessment, 2026-06-04.
- Patch
- Available – fixed in 1.26.4, 1.25.11
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:HExploitation evidence
Disclosed: evidence found.
CVE published 2 Jun 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: evidence found.
Public exploit code: GitHub proofs of concept
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors
A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), GitHub proofs of concept, the Metasploit, Exploit-DB and nuclei-templates index as of 5 Nov 2026.
What to do
Upgrade Go standard library crypto/x509 to 1.26.4 or 1.25.11.
Affected software
| Product | Affected | Fixed in |
|---|---|---|
| Go standard librarycrypto/x509 | Affected
| Fixed in
|
| Go standard librarycrypto/x509 | Affected
| Fixed in
|
Gocrypto/x509pkg:golang/crypto/x509Other threats | Affected
| Fixed in
|
Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.
AI-suggested
The vulnerability is fixed in Go standard library versions 1.25.11 and 1.26.4. Users should upgrade to these or later versions to remediate the issue. Applications and container images built with fixed Go releases are not affected. No additional mitigations are required beyond applying these updates.
Description
A vulnerability in the Go standard library crypto/x509 package causes inefficient hostname verification when processing certificates with large DNS Subject Alternative Name (SAN) lists. The VerifyHostname function repeatedly splits the hostname string for each SAN entry, leading to quadratic CPU usage growth. This can cause significant performance degradation or denial of service during TLS certificate verification, even for untrusted certificates. The issue affects Go versions before 1.25.11 and from 1.26.0 up to 1.26.3. Fixed versions are 1.25.11 and 1.26.4.
References
- go.dev/cl/783621 (opens in a new tab)
- go.dev/issue/79694 (opens in a new tab)
- groups.google.com/g/golang-announce/c/tKs3rmcBcKw (opens in a new tab)
- pkg.go.dev/vuln/GO-2026-5037 (opens in a new tab)
- access.redhat.com/security/cve/CVE-2026-27145 (opens in a new tab)
- bugzilla.redhat.com/show_bug.cgi?id=2484207 (opens in a new tab)
- security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-27145.json (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:42079 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:42080 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:68334 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:68335 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:53416 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:50319 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:54757 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:57482 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:42082 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:42150 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:42151 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:42240 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:49703 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:49702 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:53413 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:53374 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:54168 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:51187 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:46394 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:46395 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:29980 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:35832 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:34357 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:39005 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:42946 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:39573 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:38995 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:41930 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:61253 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:60354 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:57649 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:53412 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:60315 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:49712 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:53415 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:54401 (opens in a new tab)
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- access.redhat.com/errata/RHSA-2026:36317 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:54531 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:61314 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:54500 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:41030 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:44622 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:47149 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:53530 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:52946 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:66022 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:51057 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:60387 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:47737 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:60390 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:60388 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:54427 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:60391 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:60386 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:63016 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:42142 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:33574 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:23262 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:23264 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:54441 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:42644 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:36648 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:41036 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:60025 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:57488 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:54603 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:49705 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:49729 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:49744 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:49765 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:49770 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:50205 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:36797 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:42043 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:42047 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:42050 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:42051 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:42049 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:55899 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:54435 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:54525 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:57194 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:59556 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:59593 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:59557 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:54432 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:59579 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:59558 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:47735 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:59559 (opens in a new tab)