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CVE-2026-73251— Mongoose Built-in TLS: CA-bundle certificate chain accepted without any signature verification

Quick assessment

Affected
cesanta mongoose
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Mongoose 是一款嵌入式 Web 服务器和网络库。在 7.23 版本之前，针对配置了多证书 CA 证书包的 Mongoose 客户端，网络攻击者可以伪装成 TLS 服务器。在 src/tls_builtin.c 文件中， 函数将证书包存储在 中，而 仍保持为零。同时， 函数通过 接受通用名称（Common Name）匹配，但未调用 来验证证书签名。因此，伪造的自签名证书即可满足主机名检查和 CertificateVerify 检查，从而导致中间人攻击、凭证泄露、流量篡改以及恶意响应注入等安全风险。此问题已在

CVSS 9.3 · Critical EPSS 0.19% · P9

Affected Version Matrix 1

VendorProduct Version RangeStatus
cesanta mongoose < 7.23 affected
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I. Basic Information for CVE-2026-73251

Vulnerability Information
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Vulnerability Title
Mongoose Built-in TLS: CA-bundle certificate chain accepted without any signature verification
Source: CVE Program / CVE List V5
Vulnerability Description
Mongoose is an embedded web server and network library. Prior to 7.23, a network attacker can impersonate a TLS server to a Mongoose client configured with a multi-certificate CA bundle. In src/tls_builtin.c, the mg_tls_init() function stores the bundle in tls->ca_bundle_der while tls->ca_der.len remains zero, and mg_tls_recv_cert() uses tls_bundle_find() to accept a Common Name match without calling mg_tls_verify_cert_signature(). A forged self-signed certificate can therefore satisfy hostname and CertificateVerify checks and enable interception, credential disclosure, traffic modification, and malicious responses. This issue is fixed in version 7.23.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N
Source: CVE Program / CVE List V5
Vulnerability Type
证书验证不恰当
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
cesanta mongoose < 7.23 -

II. Public POCs for CVE-2026-73251

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III. Intelligence Information for CVE-2026-73251

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Patches & Fixes for CVE-2026-73251 (1)

Vendor Advisories for CVE-2026-73251 (1)

Vendor Pages for CVE-2026-73251 (1)

Same Patch Batch · cesanta · 2026-08-20 · 8 CVEs total

CVE-2026-73257 9.1 CRITICAL Mongoose: Content-Length + Transfer-Encoding coexistence enables request smuggling
CVE-2026-73256 9.1 CRITICAL Mongoose: HTTP/1.0 detection off-by-one enables request smuggling via chunked TE
CVE-2026-73253 9.1 CRITICAL Mongoose: TLS Hostname Verification Bypass via Overly Permissive Wildcard Matching
CVE-2026-73258 6.5 MEDIUM Mongoose: Multipart boundary/header scan logic error in mg_http_next_multipart
CVE-2026-73255 6.5 MEDIUM Mongoose: Path traversal in SSI #include directives enables arbitrary file read
CVE-2026-73254 5.4 MEDIUM Mongoose: Stored XSS via unescaped filenames in directory listing
CVE-2026-73259 5.4 MEDIUM Mongoose: Reflected XSS via decoded URI in directory listing render

IV. Related Vulnerabilities

Same product: mongoose
Same vendor: cesanta
Same weakness: CWE-295

V. Comments for CVE-2026-73251

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