wolfSSL up to 5.9.0 ClientHello TLSX_EchChangeSNI out-of-bounds write

CVSS Meta Temp Score
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CTI Interest Score
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7.0$0-$5k0.28-

Summaryinfo

A vulnerability categorized as critical has been discovered in wolfSSL up to 5.9.0. The affected element is the function TLSX_EchChangeSNI of the component ClientHello Handler. Such manipulation leads to out-of-bounds write. This vulnerability is traded as CVE-2026-5503. The attack may be launched remotely. There is no exploit available. A patch should be applied to remediate this issue.

Detailsinfo

A vulnerability was found in wolfSSL up to 5.9.0. It has been rated as critical. Affected by this issue is the function TLSX_EchChangeSNI of the component ClientHello Handler. The manipulation with an unknown input leads to a out-of-bounds write vulnerability. Using CWE to declare the problem leads to CWE-787. The product writes data past the end, or before the beginning, of the intended buffer. Impacted is confidentiality, integrity, and availability. CVE summarizes:

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.

The weakness was shared by Calif.io. The advisory is available at github.com. This vulnerability is handled as CVE-2026-5503 since 04/03/2026. The exploitation is known to be easy. The attack may be launched remotely. No form of authentication is required for exploitation. Technical details are known, but there is no available exploit.

Applying a patch is able to eliminate this problem. The bugfix is ready for download at github.com.

If you want to get best quality of vulnerability data, you may have to visit VulDB.

Productinfo

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Version

License

Website

CPE 2.3info

CPE 2.2info

CVSSv4info

VulDB Vector: 🔒
VulDB Reliability: 🔍

CNA CVSS-B Score: 🔒
CNA CVSS-BT Score: 🔒
CNA Vector: 🔒

CVSSv3info

VulDB Meta Base Score: 7.3
VulDB Meta Temp Score: 7.0

VulDB Base Score: 7.3
VulDB Temp Score: 7.0
VulDB Vector: 🔒
VulDB Reliability: 🔍

CVSSv2info

AVACAuCIA
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VectorComplexityAuthenticationConfidentialityIntegrityAvailability
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VulDB Base Score: 🔒
VulDB Temp Score: 🔒
VulDB Reliability: 🔍

Exploitinginfo

Class: Out-of-bounds write
CWE: CWE-787 / CWE-119
CAPEC: 🔒
ATT&CK: 🔒

Physical: No
Local: No
Remote: Yes

Availability: 🔒
Status: Not defined

EPSS Score: 🔒
EPSS Percentile: 🔒

Price Prediction: 🔍
Current Price Estimation: 🔒

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Threat Intelligenceinfo

Interest: 🔍
Active Actors: 🔍
Active APT Groups: 🔍

Countermeasuresinfo

Recommended: Patch
Status: 🔍

0-Day Time: 🔒

Patch: github.com

Timelineinfo

04/03/2026 CVE reserved
04/10/2026 +7 days Advisory disclosed
04/10/2026 +0 days VulDB entry created
04/10/2026 +0 days VulDB entry last update

Sourcesinfo

Product: github.com

Advisory: github.com
Researcher: Calif.io
Status: Confirmed

CVE: CVE-2026-5503 (🔒)
GCVE (CVE): GCVE-0-2026-5503
GCVE (VulDB): GCVE-100-356714

Entryinfo

Created: 04/10/2026 06:22
Changes: 04/10/2026 06:22 (68)
Complete: 🔍
Cache ID: 216:C94:103

If you want to get best quality of vulnerability data, you may have to visit VulDB.

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