Unauthenticated code execution via oversized certificate public key
Published Apr 2, 2026 · Updated Apr 2, 2026
Heap-based buffer overflow in Cesanta Mongoose 7.0 through 7.20 allows remote attackers to execute code via a crafted TLS 1.3 client certificate. In mg_tls_recv_cert, the built-in TLS parser copies an attacker-controlled X.509 public key into the fixed 528-byte tls->pubkey heap buffer without checking its length. Exploitation requires a TLS endpoint using the built-in TLS stack to process a peer certificate; the demonstrated chain targets mutual TLS and overwrites a connection callback to run attacker-controlled code.
Summary
What happened
Heap-based buffer overflow in Cesanta Mongoose 7.0 through 7.20 allows remote attackers to execute code via a crafted TLS 1.3 client certificate. In mg_tls_recv_cert, the built-in TLS parser copies an attacker-controlled X.509 public key into the fixed 528-byte tls->pubkey heap buffer without checking its length. Exploitation requires a TLS endpoint using the built-in TLS stack to process a peer certificate; the demonstrated chain targets mutual TLS and overwrites a connection callback to run attacker-controlled code.
The record
- CVE
- CVE-2026-5244
- Published
- Apr 2, 2026
- Updated
- Apr 2, 2026
- Vendor
- Cesanta
- Product
- Mongoose
- Classifications
- CWE-119, CWE-122, T1190
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Apr 2, 2026CVE publishedPublication date reported by the CVE source.
- Apr 2, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=7.0
- Affected versionversion=7.1
- Affected versionversion=7.10
- Affected versionversion=7.11
- Affected versionversion=7.12
- Affected versionversion=7.13
- Affected versionversion=7.14
- Affected versionversion=7.15
- Affected versionversion=7.16
- Affected versionversion=7.17
- Affected versionversion=7.18
- Affected versionversion=7.19
- Affected versionversion=7.2
- Affected versionversion=7.20
- Affected versionversion=7.3
- Affected versionversion=7.4
- Affected versionversion=7.5
- Affected versionversion=7.6
- Affected versionversion=7.7
- Affected versionversion=7.8
- Affected versionversion=7.9
What conditions does exploitation require?
What is affected?
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Weakness, pattern, technique
Public exploit references
- Crafted TLS client-certificate exploitproof of concept · demonstrated
Labels summarize the accepted research assessment. They do not indicate a test against your environment.
Technologies
Your stack
See the directory against your own environment.
Your stack
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