Critical Vulnerability in OpenSSL: Denial of Service Risk from Malicious ClientHello Messages
Summary
ALPINE-CVE-2021-3449: An OpenSSL TLS server may crash if sent a maliciously crafted renegotiation ClientHello message from a client. Affects openssl versions < 1.1.1k-r0. Fixed in 1.1.1k-r0. How to fix ↓
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Background
OpenSSL is a widely-used open-source implementation of the SSL and TLS protocols, providing cryptographic functionality for secure communication over networks. It is integral to many applications and services that require secure data transmission. The package is known for its robust features, including support for various encryption algorithms, certificate management, and secure socket layer protocols. However, OpenSSL is susceptible to vulnerabilities that can compromise its security, such as the one identified in CVE-2021-3449.
Vulnerability Detail
An OpenSSL TLS server may crash if sent a maliciously crafted renegotiation ClientHello message from a client. If a TLSv1.2 renegotiation ClientHello omits the signature_algorithms extension (which was present in the initial ClientHello) but includes a signature_algorithms_cert extension, a NULL pointer dereference will occur, leading to a crash and a denial of service attack. This vulnerability affects all OpenSSL 1.1.1 versions, and users are advised to upgrade to OpenSSL 1.1.1k to mitigate the risk. OpenSSL 1.0.2 is not impacted by this issue.
How To Fix
Minimum fixed version
1.1.1k-r0
This is the first release that contains the fix.
sudo apk add --upgrade opensslTip — Not sure which version your app runs? Vulert can match this fix to it. Scan free →
Workaround
As a temporary workaround, users can disable TLSv1.2 renegotiation on their servers until the upgrade can be performed. This may involve modifying the server configuration to restrict the use of TLSv1.2 or applying specific flags to the OpenSSL command line.
Conclusion
The vulnerability identified as CVE-2021-3449 poses a significant risk to OpenSSL users, particularly those utilizing TLSv1.2. It is crucial for users to upgrade to the patched version 1.1.1k to mitigate the risk of denial of service attacks. Regular monitoring and updates are essential for maintaining the security of applications that rely on OpenSSL.
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FAQ
CVE-2021-3449 is a vulnerability in OpenSSL that allows a denial of service attack through a maliciously crafted ClientHello message.
You can use the Vulert playground at Vulert Scanner to check if your application is affected by this vulnerability without needing to sign up.
Exploitation of this vulnerability can lead to a crash of the OpenSSL TLS server, resulting in a denial of service and potential disruption of services.
No, OpenSSL 1.0.2 is not impacted by this vulnerability; only OpenSSL 1.1.1 versions are affected.
The CVSS score for this vulnerability is 5.9, indicating a moderate level of risk.
References
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