Vulnerability · Published Apr 9, 2026 · Assigned by wolfSSL
CVE-2026-5503out-of-bounds write in TLSX_EchChangeSNI via attacker-controlled publicName
Medium 6.9
In plain English
A medium-severity out-of-bounds write in wolfSSL from wolfSSL. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.5% (higher than 45% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
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.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Alpine:v3.23 | wolfssl | 5.9.1-r0 | ALPINE-CVE-2026-5503 |
| Alpine:v3.24 | wolfssl | 5.9.1-r0 | ALPINE-CVE-2026-5503 |
| Debian:12 | wolfssl | no fix listed | DEBIAN-CVE-2026-5503 |
| Debian:13 | wolfssl | no fix listed | DEBIAN-CVE-2026-5503 |
| Ubuntu:22.04:LTS | wolfssl | no fix listed | UBUNTU-CVE-2026-5503 |
| Ubuntu:24.04:LTS | wolfssl | no fix listed | UBUNTU-CVE-2026-5503 |
| Ubuntu:25.10 | wolfssl | no fix listed | UBUNTU-CVE-2026-5503 |
| Ubuntu:26.04:LTS | wolfssl | no fix listed | UBUNTU-CVE-2026-5503 |
| Ubuntu:26.10 | wolfssl | no fix listed | UBUNTU-CVE-2026-5503 |
Affected products (as reported)
Weakness: CWE-787 · Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:L/SC:N/SI:N/SA:N