AV | This Week in Cybersecurity

2026 Week 4 Risk Direction This Week: (credential-theft + social engineering + email gateway zero-day exploitation + AI workflow attack paths)

This week’s most actionable signals surround credential-theft social engineering and high-impact perimeter/email compromise. We saw a LinkedIn “policy violation” comment-reply phishing pattern that increases the probability of account takeover for executives, recruiters, and sales teams.

On the enterprise side, responders observed PDFSider, a stealthy Windows backdoor delivered via signed PDF24 Creator EXE + malicious DLL sideloading, used in activity associated with ransomware operators and deployed in a Fortune 100 finance network.

Separately, Cisco released fixes for a maximum-severity AsyncOS flaw (CVE-2025-20393) affecting Cisco email security products, which has been exploited as a zero-day since at least late Nov 2025, elevating risk of email infrastructure compromise and downstream intrusion.

AI risk also sharpened: researchers described an indirect prompt injection pathway where a malicious calendar invite could influence Gemini to create events that expose meeting summaries in environments where attackers can view the created event.

Broader signals reinforce operational risk through third-party concentration and business interruption remain tied together, and leaders continue to report limited confidence in the third-party vendors.

Key Signals & Why They Matter

• Social platforms as an attack surface: LinkedIn comment impersonation (sometimes leveraging lnkd.in) increases successful phishing probability even for trained users.

• Email security stack is a primary choke point: Active exploitation of CVE-2025-20393 creates a “patch-now + validate compromise” imperative.

• Stealthy footholds precede ransomware: PDFSider’s memory-resident behavior, DNS comms, and side loading techniques suggest longer dwell time before ransomware monetization.

• AI workflow tools create new authorization bypass paths: Indirect prompt injection and “agent” behaviors create non-traditional exfiltration channels and policy bypass patterns.

• Third-party visibility remains weak: Industry reporting continues to show visibility gaps and downstream risk.

  
  

Threats & Campaigns Observed

PDFSider backdoor a ransomware-adjacent intrusion chain

Delivery: spearphishing ZIP with signed EXE + malicious DLL sideloading

Objective: stealthy persistent access + command execution + encrypted C2

LinkedIn “policy violation” comment-reply phishing

Delivery: bot-like LinkedIn profiles commenting “account restricted / policy violation” with external links; sometimes using lnkd.in

Cisco AsyncOS email security exploitation

Exposure: Cisco Secure Email Gateway / Secure Email and Web Manager

Impact: root-level RCE; exploited in the wild; requires patch + compromise validation

AI prompt injection via calendar invites

Mechanism: malicious payload embedded in calendar invite description; triggers when user asks AI about schedule; can result in unintended event creation and data exposure in certain enterprise configurations

Espionage targeting policy entities

LOTUSLITE campaign targeting U.S. government/policy entities via themed lures

Critical Vulnerabilities (prioritize this week)

CVE-2025-20393 (Cisco AsyncOS) - exploited as zero-day since at least late Nov 2025; patch now and rebuild on confirmed compromise.

TTPs / Detection Notes

• DLL sideloading (signed EXE loads malicious DLL) + memory-resident backdoor behavior

• DNS-based comms / port 53 used for exfil/C2 patterns (watch anomalous DNS to VPS-like endpoints)

• Social engineering through “platform authority” impersonation (policy violation / restricted access)

• Indirect prompt injection: “malicious instructions hidden in normal business content” (calendar invites / workflow artifacts)

What To Do This Week

• Patch/mitigate Cisco AsyncOS immediately: prioritize internet-facing or high-trust mail gateway roles; validate exploit exposure; follow Cisco guidance for compromise checks and rebuild if confirmed.

• Block/alert on LinkedIn phishing patterns: update awareness micro-guidance: “LinkedIn will not enforce policy via comments/external links”; increase monitoring for credential resets and anomalous sign-ins.

• Hunt for side loading artifacts: signed PDF tools + unexpected DLLs; look for unusual DLL loads and cmd execution from user context; review DNS anomalies.

• AI controls: restrict agent/tool permissions; implement “write actions” approvals; treat calendar/workflow text as untrusted input for AI summarization pipelines.

FAIR QuickQuant Scenarios

Scenario A - Email gateway compromise via CVE-2025-20393

• Loss Event Frequency (LEF): 0.5 - 2.0 / year

• Loss Magnitude (LM): $1.5M - $12M (IR + outage + data exposure + recovery)

• Annualized Loss Exposure (ALE): $750k - $24M / year

Scenario B - Exec account takeover via LinkedIn policy-violation phishing

• LEF: 0.25 - 1.0 / year

• LM: $150K - $2.5M (fraud attempts, downstream phishing, reputational + productivity)

• ALE: $37.5K - $2.5M / year

Scenario C - Stealth foothold (PDFSider) leading to ransomware

• LEF: 0.25 - 2.0 / year

• LM: $100k - $3M (business interruption + restoration + extortion)

• ALE: $25k - $6M / year

  
  

FAIR-CAM Control Mapping (controls that reduce this week’s threats)

Avoidance (↓)

• Decommission/segment internet-facing legacy email security exposures; remove direct admin interfaces from public access

• Reduce reliance on social platforms for password reset flows and sensitive workflows

Deterrence (↓)

• Strengthen identity defenses: phishing-resistant MFA for admin + executives; conditional access with impossible-travel and token binding where available

• External sender tagging + brand impersonation detections for “platform authority” scams

Resistance (↓)

• Rapid patch SLAs for KEV-like conditions; emergency change path for critical perimeter appliances

• EDR hardening for DLL sideloading + signed-binary abuse; application allowlisting for high-risk endpoints

Responsive (↓)

• Compromise validation playbooks for email gateways (rebuild triggers, golden configs)

• AI incident runbooks: prompt-injection triage, agent permission rollback, audit trails for “write actions”

Metrics To Track (board-friendly)

• % of email security appliances patched and validated (CVE-2025-20393)

• Exec/privileged accounts using phishing-resistant MFA

• Phishing reports referencing “policy violation / restricted access” themes

• Mean time to contain credential-based incidents (MTTC) vs last quarter

• Third-party outage minutes impacting critical processes (proxy for BI linkage)

Executive Talking Points (30–60 seconds)

• “This week is about identity + email infrastructure + social engineering - patching the email layer and tightening executive identity controls lowers near-term loss exposure fastest.”

• “We’re seeing stealth footholds that look like targeted backdoors before ransomware while hunting and preventing signed-binary side loading is key.”

• “AI features are increasing attack surface through language-driven manipulation that we need permission boundaries and audibility for agent actions.”