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CVE-2026-50721— IKEv1 Denial of Service via RSA-SHA1 (PKCS#1 Version 1.5 Encrypted) authentication payload

Quick assessment

Affected
The Libreswan Project libreswan
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.

The Libreswan Project libreswan是The Libreswan Project组织的一个VPN安全通信软件。 The Libreswan Project libreswan 5.3及之前版本存在安全漏洞，该漏洞源于函数RSA_authenticate_hash_signature_raw_rsa()未正确验证IKEv1数据包SIG有效载荷的认证哈希长度，可能导致远程攻击者利用bleichenbacher攻击变体在公钥指数较小（如e=3）时伪造SIG有效载荷，从而造成冒充攻击；此

CVSS 8.1 · High EPSS 0.39% · P30

Affected Version Matrix 2

VendorProduct Version RangeStatus
The Libreswan Project libreswan ≤ 5.3 affected
5.3.1 unaffected
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I. Basic Information for CVE-2026-50721

Vulnerability Information
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Vulnerability Title
IKEv1 Denial of Service via RSA-SHA1 (PKCS#1 Version 1.5 Encrypted) authentication payload
Source: CVE Program / CVE List V5
Vulnerability Description
Libreswan, via the function RSA_authenticate_hash_signature_raw_rsa(), did not correctly verify the length of the authentication hash when the SIG payload of an IKEv1 packet was encoded using PKCS #1 RSA Encryption as per RFC 2313. A remote attacker can use a variation on the Bleichenbacher attack to forge the SIG payload when small public exponents are being used (e.g., e=3), which could lead to impersonation. Additionally, a remote attacker, by encoding a shorter than expected hash in the SIG payload, could trigger an assertion leading to denial-of-service. The daemon aborts and restarts; continued exploitation causes sustained denial of service. Remote code execution is not possible. X.509 certificate verifications of remote IKE peers are not affected.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
密码学签名的验证不恰当
Source: CVE Program / CVE List V5
Vulnerability Title
The Libreswan Project libreswan 加密问题漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
The Libreswan Project libreswan是The Libreswan Project组织的一个VPN安全通信软件。 The Libreswan Project libreswan 5.3及之前版本存在安全漏洞，该漏洞源于函数RSA_authenticate_hash_signature_raw_rsa()未正确验证IKEv1数据包SIG有效载荷的认证哈希长度，可能导致远程攻击者利用bleichenbacher攻击变体在公钥指数较小（如e=3）时伪造SIG有效载荷，从而造成冒充攻击；此
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
The Libreswan Project libreswan 0 ~ 5.3 -

II. Public POCs for CVE-2026-50721

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III. Intelligence Information for CVE-2026-50721

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Vendor Advisories for CVE-2026-50721 (3)

Same Patch Batch · The Libreswan Project · 2026-07-02 · 3 CVEs total

CVE-2026-50722 8.1 HIGH IKEv2 Denial of Service via RSA-SHA1 (PKCS#1 RSASSA-PKCS1-v1_5) authentication payload
CVE-2026-12413 7.5 HIGH IKEv2 Denial of Service via malformed fragmentation

IV. Related Vulnerabilities

Same product: libreswan
Same vendor: The Libreswan Project
Same weakness: CWE-347

V. Comments for CVE-2026-50721

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