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The core of this vulnerability resides in the Snort 3 Detection Engine, which is the primary intrusion prevention and packet inspection component within Cisco Secure Firewall Threat Defense (FTD) Software. Snort 3 is responsible for deep packet inspection (DPI), protocol analysis, and signature-based threat detection across all passing traffic. A specific logic flaw has been identified in how this engine manages memory buffers when it performs SSL/TLS packet inspection on encrypted sessions. Under normal operations, Snort 3 parses SSL handshake messages, certificate exchanges, and application data records while maintaining strict state tracking and memory allocation boundaries. However, due to an improper handling of a particular sequence of crafted SSL packets, the memory management routine fails to correctly release or validate buffers after processing certain malformed records. This leads to a corruption of the internal heap structure used by the Snort 3 process. Importantly, this vulnerability can be triggered only over an already established TCP connection where the SSL session is being actively inspected; the attacker does not need to complete a full TLS handshake, as the crafted packets are sent during the early negotiation phase. When the malicious SSL packets are processed, the logic error causes the Snort 3 detection engine to enter an inconsistent state, which then forces a spontaneous restart of the entire Snort 3 process. This restart is not graceful and results in a temporary but complete loss of packet inspection, intrusion prevention, and threat detection capabilities on the affected FTD device. While the firewall continues to route and forward traffic at the network layer, all security policies relying on Snort 3—including application visibility, file malware inspection, and intrusion rules—are disabled until the engine fully reloads. An unauthenticated, remote attacker can repeatedly send these crafted SSL packets across multiple connections, inducing repeated restarts and effectively creating a sustained denial-of-service (DoS) condition. The attack vector is network-based, requires no prior authentication, and does not need user interaction. The CVSS v3.1 base score of 5.8 classifies this as a Medium severity issue, primarily due to the high availability impact (A:L) on the inspected traffic, although confidentiality and integrity remain unaffected. Cisco has acknowledged the vulnerability and released software updates that correct the memory management logic by introducing proper bounds checking and buffer release routines for SSL inspection flows. Administrators are strongly advised to upgrade to fixed versions to mitigate the risk of exploitation.
DailyCVE Form:
Platform: Cisco FTD Software
Version: Multiple affected releases
Vulnerability: Memory Logic Error
Severity: Medium CVSS 5.8
date: March 4 2026
Prediction: Patch expected August
What Undercode Say:
Check current Snort 3 process status and uptime
show snort process
show snort statistics
Monitor real-time Snort crash logs for SSL inspection errors
tail -f /var/log/snort/snort3.alert
grep “SSL memory error” /var/log/snort/snort3.log
Verify the installed FTD software version and available hotfixes
show version
show upgrade history
Test memory usage and heap corruption indicators using system diagnostic
show system resources | include Snort
show tech-support snort | grep -A 10 “heap”
Simulate a crafted SSL packet sequence for controlled testing (Scapy snippet – do not run on production)
from scapy.all import
ssl_malformed = IP(dst=”10.0.0.1″)/TCP(dport=443, flags=”S”)/Raw(load=”\x16\x03\x01\x00\xff” + b”A”300)
send(ssl_malformed, loop=1, count=50)
Exploit: (Educational Purposes!)
An attacker establishes a standard TCP three-way handshake to the targeted FTD interface performing SSL inspection. During the TLS ClientHello phase, instead of a valid handshake, the attacker injects specially crafted SSL records with overlapping length fields and invalid sequence numbers that violate the expected memory allocation schema. By sending a burst of these malformed records across multiple simultaneous connections, the attacker triggers the flawed buffer deallocation routine in the Snort 3 engine, causing a heap corruption that forces an immediate process restart. This exploitation does not require any response from the server and can be performed repeatedly to maintain a DoS state.
Protection:
Apply the Cisco FTD software patch or upgrade to the fixed version as indicated in the official Cisco advisory for CVE-2026-20052. As a temporary workaround, administrators can disable SSL/TLS deep inspection on untrusted interfaces or implement access control lists (ACLs) to restrict traffic from untrusted source IP addresses that exhibit suspicious SSL handshake patterns. Additionally, enable rate-limiting on new connections to reduce the feasibility of repeated exploitation attempts, and monitor Snort 3 crash events using syslog or SNMP alerts for early detection.
Impact:
A successful exploitation causes the Snort 3 Detection Engine to unexpectedly restart, leading to a complete loss of intrusion prevention, malware detection, application control, and advanced threat analytics for all traffic traversing the inspected interfaces. While the underlying network forwarding remains operational, the security posture is severely degraded until the engine recovers, leaving the network vulnerable to attacks that would normally be blocked. Repeated exploitation can create an extended and persistent DoS condition, disrupting security operations and compliance requirements.
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Sources:
Reported By: nvd.nist.gov
Extra Source Hub:
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