CVE-2023-2650 Overview
CVE-2023-2650 is a Denial of Service vulnerability in OpenSSL that affects the processing of specially crafted ASN.1 object identifiers. Applications that use OBJ_obj2txt() directly or utilize OpenSSL subsystems such as OCSP, PKCS7/SMIME, CMS, CMP/CRMF, or TS without message size limits may experience significant delays when processing malicious messages, leading to service disruption.
The vulnerability stems from the way OpenSSL translates ASN.1 OBJECT IDENTIFIERs from DER encoding form to their canonical numeric text representation. When a sub-identifier within the OBJECT IDENTIFIER is excessively large (tens or hundreds of KiBs), the translation to decimal text exhibits O(n²) time complexity, where 'n' represents the size of the sub-identifiers in bytes.
Critical Impact
Network-accessible applications using affected OpenSSL functions can be forced into extended processing delays, causing Denial of Service conditions that impact availability of TLS services, certificate validation, and cryptographic operations.
Affected Products
- OpenSSL 3.0.x, 3.1.x (impacts OCSP, PKCS7/SMIME, CMS, CMP/CRMF, TS subsystems)
- OpenSSL 1.1.1 and 1.0.2 (limited impact on display functions)
- Debian Linux 10.0 and 11.0
Discovery Timeline
- May 30, 2023 - CVE-2023-2650 published to NVD
- March 19, 2025 - Last updated in NVD database
Technical Details for CVE-2023-2650
Vulnerability Analysis
The vulnerability exists in OpenSSL's handling of ASN.1 OBJECT IDENTIFIERs, which are composed of a series of sub-identifiers without inherent size limits. The OBJ_obj2txt() function translates these identifiers from DER encoding to decimal text form. When processing sub-identifiers of absurdly large sizes, the conversion algorithm's quadratic time complexity causes severe performance degradation.
In OpenSSL 3.0 and newer versions, the introduction of string-based cryptographic algorithm fetching expanded the attack surface significantly. OBJECT IDENTIFIERs in canonical numeric text form can be used as identifiers for fetching algorithms through the AlgorithmIdentifier ASN.1 structure, which is ubiquitous in cryptographic protocols for specifying signing, verification, encryption, decryption, and digest algorithms.
The impact varies by OpenSSL version. OpenSSL 3.0+ is affected across multiple subsystems including X.509 certificate processing and signature verification. For TLS connections, the impact is mitigated by the 100KiB limit on peer certificate chains, and primarily affects clients or servers with explicit client authentication enabled. Earlier versions (1.1.1 and 1.0.2) are affected only in display operations and are considered low severity.
Root Cause
The root cause is an inefficient algorithm in the OBJ_obj2txt() function that exhibits O(n²) time complexity when converting large sub-identifiers to decimal text representation. The lack of input validation or size limits on individual sub-identifiers within OBJECT IDENTIFIERs allows attackers to craft malicious inputs that trigger worst-case algorithmic behavior, consuming excessive CPU resources during the conversion process.
Attack Vector
An attacker can exploit this vulnerability by sending specially crafted ASN.1 data containing OBJECT IDENTIFIERs with extremely large sub-identifiers to a vulnerable application. Attack vectors include:
- Sending malformed X.509 certificates during TLS handshakes
- Submitting crafted OCSP requests or responses
- Providing malicious PKCS7/SMIME, CMS, or CMP/CRMF messages
- Exploiting timestamp (TS) protocol implementations
The attack requires no authentication and can be executed remotely over the network, though user interaction may be required depending on the application context. The vulnerability does not compromise confidentiality or integrity—it specifically targets availability through resource exhaustion.
When processing a malicious OBJECT IDENTIFIER, the OBJ_obj2txt() function enters an extended computation loop. For example, an attacker could embed an oversized sub-identifier within an AlgorithmIdentifier structure in a certificate's signature algorithm field. When the application attempts to validate the certificate or translate the algorithm identifier, the quadratic processing time causes the application to become unresponsive.
Detection Methods for CVE-2023-2650
Indicators of Compromise
- Abnormally high CPU utilization on systems running OpenSSL-dependent services
- Extended response times or timeouts when processing TLS connections or certificates
- Application logs showing delays in certificate validation or cryptographic operations
- Unusual ASN.1 parsing errors or warnings in OpenSSL diagnostic output
Detection Strategies
- Monitor system resource utilization for processes handling TLS/SSL connections
- Implement network-level detection for anomalously large ASN.1 structures in certificate exchanges
- Deploy application performance monitoring to identify sudden latency spikes in cryptographic operations
- Review OpenSSL debug logs for extended processing times in OBJ_obj2txt() operations
Monitoring Recommendations
- Configure alerting for CPU consumption anomalies on web servers, mail servers, and TLS termination points
- Implement request timeout monitoring for services that process X.509 certificates or PKCS7 messages
- Track certificate validation duration metrics to establish baselines and detect deviations
- Monitor connection queue depths for TLS-enabled services to identify potential DoS conditions
How to Mitigate CVE-2023-2650
Immediate Actions Required
- Update OpenSSL to patched versions: 3.1.1, 3.0.9, or 1.1.1u
- Review and restrict message size limits for applications using OCSP, PKCS7/SMIME, CMS, CMP/CRMF, or TS subsystems
- Implement connection timeouts and rate limiting on TLS-enabled services
- Audit applications for direct calls to OBJ_obj2txt() with untrusted data
Patch Information
OpenSSL has released patches addressing this vulnerability across multiple branches. The fixes implement improved algorithmic efficiency and input validation in the OBJ_obj2txt() function. Refer to the OpenSSL Security Advisory 20230530 for official guidance.
Specific commits addressing this issue:
Debian users should refer to DSA-5417 and the Debian LTS Announcement for distribution-specific updates.
Workarounds
- Implement strict message size limits for protocols using affected OpenSSL subsystems
- Configure application-level timeouts for certificate validation and cryptographic operations
- Deploy reverse proxy or WAF rules to filter requests containing anomalously large ASN.1 structures
- For TLS servers, ensure client authentication is disabled if not strictly required
# Verify OpenSSL version and check for vulnerability
openssl version -a
# Recommended: Update to patched version
# For Debian/Ubuntu
sudo apt update && sudo apt upgrade openssl libssl1.1 libssl3
# For RHEL/CentOS
sudo yum update openssl
# Verify updated version
openssl version
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
