(D)TLS 1.2 client accepts early ChangeCipherSpec before ClientKeyExchange

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-93304
StatePUBLISHED
AssignerwolfSSL
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-09-27 10:16:59 UTC
Updated2026-09-27 10:16:59 UTC
DescriptionA (D)TLS 1.2 client can accept a ChangeCipherSpec message before it has sent its ClientKeyExchange. No master secret has been derived at that point, so the client installs read keys derived from a known (deterministic) key and checks the server's Finished against that same key. An out-of-order ChangeCipherSpec can therefore be used by an attacker to complete the handshake in place of the server and send data the client accepts as authentic. The client's own traffic still uses correctly derived keys, so the attacker cannot read it, and the genuine server never completes the handshake. DTLS 1.2 clients are exposed because a datagram read can deliver the out-of-order records on its own. TLS 1.2 clients are exposed when the application supplies received bytes with wolfSSL_inject() or enables read ahead. For certificate suites, the attacker must be in a man-in-the-middle position. For PSK (Pre Shared Key) connections, any fake server can succeed without knowing the PSK.

Risk And Classification

Primary CVSS: v4.0 6.3 MEDIUM from [email protected]

CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

Problem Types: CWE-696 | CWE-696 CWE-696 Incorrect Behavior Order

VersionSourceTypeScoreSeverityVector
4.0[email protected]Secondary6.3MEDIUMCVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/E:X/C...
4.0CNACVSS6.3MEDIUMCVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N

CVSS v4.0 Breakdown

Attack Vector
Network
Attack Complexity
High
Attack Requirements
Present
Privileges Required
None
User Interaction
None
Confidentiality
None
Integrity
Low
Availability
None
Sub Conf.
None
Sub Integrity
None
Sub Availability
None

CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA WolfSSL WolfSSL affected 4.7.0 5.9.2 semver Not specified

References

ReferenceSourceLinkTags
github.com/wolfSSL/wolfssl/pull/11458 [email protected] github.com
CVE Program record CVE.ORG www.cve.org canonical
NVD vulnerability detail NVD nvd.nist.gov canonical, analysis

Vendor Comments And Credit

Discovery Credit

CNA: Anthropic OSS program (en)

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