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CVE-2026-63073— Untrusted Sender DN Used as Format String in CMP Response Validation

Quick assessment

Affected
OpenSSL OpenSSL
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.

OpenSSL是OpenSSL团队开源的一个提供安全通信加密功能的软件库。 OpenSSL 4.0.0至4.0.2之前版本、3.6.0至3.6.4之前版本、3.5.0至3.5.8之前版本和3.4.0至3.4.7之前版本存在格式化字符串错误漏洞，该漏洞源于CMP响应验证过程中将发送者可区分名称直接作为格式字符串传递给ERR_raise_data()，可能导致恶意或拦截的CMP端点使CMP客户端崩溃，造成拒绝服务。

AI Predicted 6.5 Difficulty: Easy EPSS 1.16% · P67

Possible ATT&CK Techniques 1 AI

T1190 · Exploit Public-Facing Application

Affected Version Matrix 4

VendorProduct Version RangeStatus
OpenSSL OpenSSL 4.0.0< 4.0.2 affected
3.6.0< 3.6.4 affected
3.5.0< 3.5.8 affected
3.4.0< 3.4.7 affected
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I. Basic Information for CVE-2026-63073

Vulnerability Information
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Vulnerability Title
Untrusted Sender DN Used as Format String in CMP Response Validation
Source: CVE Program / CVE List V5
Vulnerability Description
Issue summary: OpenSSL CMP response validation passed an unexpected response sender distinguished name directly as the format string to `ERR_raise_data()`. Impact summary: A malicious or intercepted CMP endpoint can crash a CMP client that enforces an expected sender or uses a pinned server certificate whose subject becomes the default expected sender. CWE: CWE-134 (Use of Externally-Controlled Format String) Description: When validating a received CMP message, ossl_cmp_msg_check_update() converts the peer-supplied sender distinguished name with X509_NAME_oneline() and passes it directly as the format argument to ERR_raise_data(). Percent characters survive the conversion, so a sender DN such as "CN=%s%n" reaches BIO_vsnprintf() as an attacker-controlled format string with no matching variadic arguments. This path is only reached when the caller configures an expected sender or pins a server certificate, which is the normal configuration for a CMP client validating server responses. Since the attacker controls the format string but none of the variadic arguments, such specifiers as %s and %n dereference or write through unrelated stack contents and crash the client. The reliable consequence is a denial of service, when the response comes from a malicious or intercepted CMP endpoint. There is no controlled memory write, arbitrary-address read, or reliable path to remote code execution. FIPS impact: no No FIPS modules are affected by this issue, as the CMP protocol implementation is outside the OpenSSL FIPS module boundary.
Source: CVE Program / CVE List V5
CVSS Information
N/A
Source: CVE Program / CVE List V5
Vulnerability Type
使用外部控制的格式字符串
Source: CVE Program / CVE List V5
Vulnerability Title
OpenSSL 格式化字符串错误漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
OpenSSL是OpenSSL团队开源的一个提供安全通信加密功能的软件库。 OpenSSL 4.0.0至4.0.2之前版本、3.6.0至3.6.4之前版本、3.5.0至3.5.8之前版本和3.4.0至3.4.7之前版本存在格式化字符串错误漏洞，该漏洞源于CMP响应验证过程中将发送者可区分名称直接作为格式字符串传递给ERR_raise_data()，可能导致恶意或拦截的CMP端点使CMP客户端崩溃，造成拒绝服务。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
OpenSSL OpenSSL 4.0.0 ~ 4.0.2 -

II. Public POCs for CVE-2026-63073

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III. Intelligence Information for CVE-2026-63073

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Patches & Fixes for CVE-2026-63073 (4)

Vendor Advisories for CVE-2026-63073 (1)

Same Patch Batch · OpenSSL · 2026-08-25 · 9 CVEs total

CVE-2026-75803 AEAD Forgeries with Empty Ciphertext When Using EVP_Cipher()
CVE-2026-18798 QUIC Server May Trigger Double Free When Processing INITIAL Packet
CVE-2026-54874 Excessive Memory Use Buffering DTLS Records for a Future Epoch
CVE-2026-63074 CMP Indefinite Cache Growth of ExtraCerts
CVE-2026-63072 Heap Buffer Overflow in CMS Key Unwrapping
CVE-2026-63075 QUIC ACK-only Packet Retention Can Cause Memory Exhaustion
CVE-2026-63076 Invalid Pointer Dereference in CMP Server via Crafted protectionAlg
CVE-2026-14457 RPK Server Signature Algorithm Selection Can Dereference a Missing Certificate

IV. Related Vulnerabilities

Same product: OpenSSL
Same vendor: OpenSSL
Same weakness: CWE-134

V. Comments for CVE-2026-63073

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