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CVE-2026-5503

Wolfssl buffer overflow

9.1 CRITICALEPSS 0.45%
  1. Published9 Apr 2026

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.

CVSS 3.1 breakdown

Attack vectorNetwork
Attack complexityLow
Privileges requiredNone
User interactionNone
ScopeUnchanged
ConfidentialityNone
IntegrityHigh
AvailabilityHigh
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H

Affected products

Wolfssl≤ 5.9.0

Remediation

No fixed version is recorded in the NVD data. Check the vendor advisory for the latest guidance.

References

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Frequently asked

Is CVE-2026-5503 being actively exploited?

CVE-2026-5503 is not in the CISA KEV catalog. Its EPSS exploit probability is 0.45%.

How severe is CVE-2026-5503?

CVE-2026-5503 has a CVSS 3.1 base score of 9.1, rated critical. EPSS estimates a 0.45% probability of exploitation.

Which products are affected by CVE-2026-5503?

Affected products include Wolfssl.

How do I fix CVE-2026-5503?

Apply the vendor's patch or advisory guidance, then verify no affected versions remain across your devices.

How Secuno handles this

Secuno correlates vulnerabilities like CVE-2026-5503 against the real software inventory on every managed device, as each hourly inventory arrives. Rather than a static severity, each match is scored in context: exploit availability, EPSS, the asset's exposure, and business criticality decide where it lands in the queue. If an affected version is present anywhere across your portfolio, it surfaces automatically with a prioritised remediation path.

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Data from the NVD, CISA KEV catalog and FIRST EPSS. CVSS 3.1 base score shown where available.