High severity · published Aug 13, 2026
CVE-2026-56862
Limit handshake messages we are willing to accept post-handshake in crypto/tls
7.5
CVSS
0.6%
EPSS
No
On KEV
Description
Handshake messages, such as KeyUpdate, are always considered as state-advancing, regardless of whether a handshake has been completed or not. As a result, a malicious client can keep sending KeyUpdate messages to force the server to keep performing key derivation operations indefinitely.
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Confidentiality
None
Integrity
None
Availability
High
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.6% · higher than 47% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
CR
crypto/tls · Go standard library
before 1.25.13; 1.26.0-0 before 1.26.6; 1.27.0-0 before 1.27.0-rc.3 · source: vendor
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-56862
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-56862
go.dev
https://go.dev/cl/804261
go.dev
https://go.dev/issue/80528
groups.google.com
https://groups.google.com/g/golang-announce/c/94pEornpRlI
pkg.go.dev
https://pkg.go.dev/vuln/GO-2026-6090
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