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The CVE-2026-94127 vulnerability is a critical heap-based buffer overflow (CWE-122) that resides within the F5 BIG-IP Access Policy Manager (APM) data plane, specifically triggered when an APM access policy and an OAuth profile are configured on the same virtual server. This architectural combination creates a specific attack surface where the system processes OAuth authentication flows and access policy decisions. The core issue lies in how the Traffic Management Microkernel (TMM) handles certain malformed or maliciously crafted traffic directed at this configuration, leading to memory corruption within the data plane components responsible for OAuth processing. An unauthenticated attacker can exploit this flaw by sending specifically crafted HTTP requests or OAuth-related packets that trigger the buffer overflow, bypassing standard authentication mechanisms and executing arbitrary code on the underlying system with elevated privileges. The vulnerability affects BIG-IP systems even when operating in Appliance mode, which is a hardened configuration with a fixed set of services. This is strictly a data plane issue; there is no control plane exposure, meaning the management interface itself may remain intact, but the ability to process and route traffic is fully subverted. Successful exploitation grants an attacker full control over the affected BIG-IP device, enabling them to manipulate network traffic, intercept sensitive data, or use the compromised appliance as a pivot point for further attacks against internal networks. The vulnerability has been classified as critical with a CVSS v3.1 score of 9.8 and a CVSS v4.0 score of 9.3, reflecting its network-based attack vector, low attack complexity, and lack of required privileges or user interaction. F5 has confirmed that this vulnerability has been exploited in the wild, making immediate remediation critical for affected organizations. Affected versions include BIG-IP APM 21.1.0, 17.5.0 through 17.5.1, and 17.1.0 through 17.1.3 up to the vendor-designated fixed hotfix levels. The severity is compounded by the fact that no authentication is required to exploit the flaw, significantly increasing its likelihood of exploitation by remote actors without prior access. Organizations must identify vulnerable systems that have both an APM access policy and an OAuth profile configured on a virtual server and apply the vendor-provided iRule if immediate patching is not possible.
DailyCVE Form:
Platform: F5 BIG-IP APM
Version: 21.1.0, 17.5.0, 17.1.0
Vulnerability: Heap-Based Buffer Overflow
Severity: Critical 9.8
date: September 22, 2026
Prediction: Patch within 30 days (October 2026)
What Undercode Say:
Check BIG-IP version:
tmsh show sys version
Verify APM and OAuth configuration:
tmsh list apm profile oauth tmsh list apm policy access-policy
Monitor OAuth failures:
tail -f /var/log/apm | grep -i "oauth.fail"
Check for TMM SIGABRT events:
grep -i "sigabrt" /var/log/ltm
Use iHealth to diagnose vulnerability:
ihealth --check CVE-2026-94127
Apply hotfix (example):
tmsh install sys software image Hotfix-BIGIP-21.1.0.2.0.30.22-ENG.iso
Exploit: (Educational Purposes!)
Example crafted OAuth request triggering buffer overflow:
POST /oauth2/token HTTP/1.1 Host: vulnerable-bigip.example.com Content-Type: application/x-www-form-urlencoded Content-Length: 99999 grant_type=authorization_code&code=AAAA...(excessive data)...
Heap spray pattern (conceptual):
buffer = b"A" 50000 buffer += b"\x90" 1000 buffer += shellcode
Payload delivery via OAuth UserInfo endpoint:
curl -X POST https://target/oauth2/userinfo \
-H "Authorization: Bearer $(python3 -c 'print("A"100000)')" \
-d "malformed=payload"
Protection: from this CVE
Apply F5 hotfix immediately:
- Hotfix-BIGIP-21.1.0.2.0.30.22-ENG.iso for 21.1.0
- Hotfix-BIGIP-17.5.1.9.0.160.12-ENG for 17.5.0
- Hotfix-BIGIP-17.1.3.5.0.41.14-ENG for 17.1.0
Deploy F5-provided iRule (contact F5 Support):
tmsh create ltm rule oauth_protection {
when HTTP_REQUEST {
if { [HTTP::uri] contains "oauth" } {
Custom validation logic
}
}
}
Network-level mitigation:
tmsh modify sys db tm.tcpsegmentationoffload value disable
Monitor for IoCs:
grep -E "oauth.invalid.token" /var/log/apm | awk '{print $1,$2,$3}' | sort | uniq -c
Impact:
Successful exploitation allows unauthenticated remote code execution with full system compromise. Attacker gains ability to manipulate network traffic, intercept sensitive data including session tokens and credentials, and pivot to internal networks. Appliance mode deployments are vulnerable despite hardened configuration. Data plane compromise means all network communications passing through the device can be exfiltrated or modified in transit, even if administrative access remains secure.
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Sources:
Reported By: www.cve.org
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