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Vulnerabilities

Vulnerability · CVE-2026-5503

In TLSX_EchChangeSNI, the ctx->extensions branch set extensions unconditionally even when TLSX_Find returned NULL.

Published Apr 9, 2026 · catalog updated Jun 17, 2026 · In TLSX_EchChangeSNI, the ctx->extensions

Check if you run it

No confirmed exploitation is on record for CVE-2026-5503. EPSS is 0.45%. Act only if a listed version of In TLSX_EchChangeSNI, the ctx->extensions is installed.

Gaps on this record

  • The stored product name is a package slug. The name on this page is taken from the title (In TLSX_EchChangeSNI, the ctx->extensions).
  • No version range is stored. A customer cannot check an installed version against this record.
  • No vendor fix or required action is stored. Compare the linked advisory before you change production.
Severity
Medium6.9
Known exploitation
Not in CISA/VulnCheck KEV
EPSS
0.45%
Remediation
Not established
Affected products
cpe wolfssl/wolfssl

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.

Are you affected?

Enter the version you run. The result uses only the ranges stored on this record.

The check returns affected, not affected, or incomplete. It does not guess a version that is missing from the record.

  • cpe wolfssl/wolfsslversion unspecified

How to fix CVE-2026-5503

What to do

Three questions, each answered from this record only. Confirm the vendor advisory before you patch.

Should you patch?

No confirmed exploitation is on record for CVE-2026-5503. EPSS is 0.45%. Act only if a listed version of In TLSX_EchChangeSNI, the ctx->extensions is installed.

Which versions are affected?

Affected version ranges are not on this record. Compare the installed version with the linked vendor advisory before you change production.

What should an analyst verify?

CWE-787: Out-of-bounds Write. EPSS 0.45%. There is no CISA KEV listing. No Exploit-DB or Metasploit reference is linked. Use the source links for the original advisory.

Code

The project this record applies to. Exploit listings stay in References.

Timeline

Detection, updates, and resolution for this record.

  1. Apr 9, 2026 · NIST NVD

    Detected

    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

  2. Jun 17, 2026 · NIST NVD

    Updated

    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

Sources

  • CVE.orgVulnerability recordCVE-2026-5503

    Official CVE identifier

    cve.org
  • FIRST EPSSExploitation probabilityCVE-2026-5503

    30-day exploitation probability 0.5%

    first.org
  • NIST NVDVulnerability recordCVE-2026-5503

    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 cl

    nvd.nist.gov

References

Freshness

Last verified in this catalog Oct 18, 2026. Significant claims (KEV, EPSS, CVSS, affected ranges) come from the source rows above — open the original publisher for the authoritative advisory.