CVE-2026-5503 out-of-bounds write in TLSX_EchChangeSNI via attacker-controlled publicName
An out-of-bounds write in wolfSSL's TLS extension handling allows attackers to corrupt memory, potentially leading to code execution or crashes.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-5503?
CVE-2026-5503 is a medium-severity memory corruption vulnerability in Wolfssl Wolfssl, published on 9 Apr 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
In TLSX_EchChangeSNI, the ctx->extensions branch set extensions unconditionally even when TLSX_Find returned NULL. This caused TLSX_UseSNI to attach the attacker-controlled publicName to the shared WOLFSSL_CTX when no inner SNI was configured. TLSX_EchRestoreSNI then failed to clean it up because its removal was gated on serverNameX != NULL. The inner ClientHello was sized before the pollution but written after it, causing TLSX_SNI_Write to memcpy 255 bytes past the allocation boundary.
Weakness: CWE-787
Which versions are affected by CVE-2026-5503?
It affects 1 product.
Products include Wolfssl Wolfssl.
How do I fix CVE-2026-5503?
Apply the vendor's patch.
Upgrade to the fixed version. Memory-safe languages, compiler hardening and fuzzing prevent most new cases. More about Memory corruption.
Is CVE-2026-5503 being exploited?
There is no known exploitation of CVE-2026-5503 in the wild and no public exploit code.
Other vulnerabilities in Wolfssl Wolfssl
Sources
Also known as DEBIAN-CVE-2026-5503, GHSA-65xm-pfx9-g5p3, JLSEC-2026-731, UBUNTU-CVE-2026-5503.