CVE-2026-5503: In TLSX_EchChangeSNI, the ctx->extensions branch set extensions unconditionally even when TLSX_Find returned N

Q: How do I fix CVE-2026-5503?

wolfssl: upgrade to newer than 5.9.0. Exact commands for each OS are on this page.

Q: Is CVE-2026-5503 being exploited?

CVE-2026-5503 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2026-5503 affect?

CVE-2026-5503 affects wolfssl. Severity is critical (CVSS 9.1). 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 configur

This month

CRITICAL 9.1REMOTEUPGRADE

CVE-2026-5503 is a critical-severity flaw (CVSS 9.1) affecting wolfssl. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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 memcp

Why this priority

Critical severity
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	9.1 (Critical)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.5% (top 57%)
CISA exploited list	No
Weakness	CWE-787
Published	2026-04-09
Last modified	2026-06-17

Publisher (CNA): wolfSSL Inc. · Vendor: wolfssl

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-04-09 23:17 UTCPublished CVE record published
2026-06-17 10:59 UTCUpdated Record last modified

wolfssl wolfssl UPGRADE

Affected: <= 5.9.0

Fixed in: newer than 5.9.0

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy wolfssl || rpm -q wolfssl || wolfssl --version

2. UPGRADE to newer than 5.9.0 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade wolfssl

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade wolfssl

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-5503?

wolfssl: upgrade to newer than 5.9.0. Exact commands for each OS are on this page.

Is CVE-2026-5503 being exploited?

CVE-2026-5503 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-5503 affect?

CVE-2026-5503 affects wolfssl. Severity is critical (CVSS 9.1). 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 configur

How urgent is CVE-2026-5503?

Priority 48/100. Critical severity; Remotely exploitable, no login, no user action

Software pages

wolfSSL vulnerabilities

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References

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