CVE-2026-3849
Published: 19 March 2026
Description
Stack Buffer Overflow in wc_HpkeLabeledExtract via Oversized ECH Config. A vulnerability existed in wolfSSL 5.8.4 ECH (Encrypted Client Hello) support, where a maliciously crafted ECH config could cause a stack buffer overflow on the client side, leading to potential remote…
more
execution and client program crash. This could be exploited by a malicious TLS server supporting ECH. Note that ECH is off by default, and is only enabled with enable-ech.
Mitigating Controls (NIST 800-53 r5)AI
SI-2 ensures timely patching of the wolfSSL library to address the specific stack buffer overflow in wc_HpkeLabeledExtract.
SI-16 implements memory protections like stack canaries and DEP to mitigate exploitation of the stack buffer overflow even if unpatched.
SI-10 enforces validation of ECH configuration inputs to prevent oversized inputs from triggering the buffer overflow in wc_HpkeLabeledExtract.
Security SummaryAI
CVE-2026-3849 is a stack buffer overflow vulnerability (CWE-787) in the wc_HpkeLabeledExtract function within wolfSSL version 5.8.4's Encrypted Client Hello (ECH) support. A maliciously crafted, oversized ECH configuration can trigger the overflow on the client side, potentially leading to remote code execution or client program crashes.
The vulnerability can be exploited by a malicious TLS server that supports ECH, targeting clients with ECH enabled via the enable-ech option. Attackers require only network access to the victim client, with no privileges, user interaction, or special conditions needed, as reflected in the CVSS 3.1 score of 9.8 (AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H). Successful exploitation could allow arbitrary code execution or denial of service through crashes.
A patch addressing this issue is available in wolfSSL's GitHub pull request #9737. ECH functionality is disabled by default in wolfSSL, requiring explicit enabling, which limits exposure.
Details
- CWE(s)
Affected Products
MITRE ATT&CK Enterprise TechniquesAI
Why these techniques?
Stack buffer overflow in client-side wolfSSL ECH processing enables remote exploitation for code execution (T1203) or application crashes causing DoS (T1499.004).