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Cisco Secure Firewall Adaptive Security Appliance (ASA) and Secure Firewall Threat Defense (FTD) Buffer Overflow Vulnerability

Exploited · KEV 2025-09-25CVE-2025-20333CWE-120

Exploited since 2025-09-25. 2 of 8 rule sources name it; Cloudflare blocks by default.

Edge rules
2/8
Our test
No exploit yet
CVSS
9.9
EPSS
71.2% Top 0.6%
Posts, 14d
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Published
2025-09-25
A vulnerability in the VPN web server of Cisco Secure Firewall Adaptive Security Appliance (ASA) Software and Cisco Secure Firewall Threat Defense (FTD) Software could allow an authenticated, remote attacker to execute arbitrary code on an… More

A vulnerability in the VPN web server of Cisco Secure Firewall Adaptive Security Appliance (ASA) Software and Cisco Secure Firewall Threat Defense (FTD) Software could allow an authenticated, remote attacker to execute arbitrary code on an affected device. This vulnerability is due to improper validation of user-supplied input in HTTP(S) requests. An attacker with valid VPN user credentials could exploit this vulnerability by sending crafted HTTP requests to an affected device. A successful exploit could allow the attacker to execute arbitrary code as root, possibly resulting in the complete compromise of the affected device.

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Ask about CVE-2025-20333: who's covered, what to patch first, how vendors compare. I cite sources and won't help with attacks.

Workers AI (Llama 3.3). Can be wrong: check the cited source.

Severity, decoded

CVSS 3.1
Critical · 9.9 / 10

Exploitable over the network, with low privileges and no user interaction, leading to full loss of confidentiality, integrity and availability, and the impact can reach components beyond the vulnerable one.

Over the internetAny user loginNo user actionWorks reliablySpreads beyond the appFull compromise
How the score is built8 metrics
  • Attack vectorAn attacker can reach it over the internet; no access to your network needed.
    Network
  • Attack complexityNo special conditions are needed; the attack works reliably.
    Low
  • Privileges requiredThe attacker needs an ordinary user account.
    Low
  • User interactionNo one has to click or open anything; the attack works on its own.
    None
  • ScopeThe attack can spread beyond the vulnerable component to other parts of the system.
    Changed
  • Confidentiality impactAn attacker can read all data the affected component holds, or the most sensitive parts of it.
    High
  • Integrity impactAn attacker can change any data or files the affected component protects.
    High
  • Availability impactAn attacker can take the component down completely or keep it from serving anyone.
    High
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H
CISA's assessmentSSVC, from the CVE record
ExploitationActive

Attackers are exploiting this in the wild.

AutomatableNo

At least one step needs hands-on work, which slows mass attacks.

Technical impactTotal

A successful attack gives full control over the affected software or all of its data.

Public exploits

None found
0 Metasploit0 Exploit-DB0 Scanner template0 GitHub PoCs

No exploit in Exploit-DB or Metasploit, and no scanner template. That lowers, but doesn't remove, the chance of mass exploitation.

Timeline

  1. 2025-09-25
    CVE published
    CVE List
  2. 2025-09-25
    Added to CISA KEV
    Confirmed exploitation in the wild
  3. 2025-09-28
    Cloudflare ships a rule
    Cisco Secure Firewall Adaptive Security Appliance - Remote Code Execution - CVE:CVE-2025-20333, CVE:CVE-2025-20362, CVE:CVE-2025-20363
  4. 2025-12-03
    F5 ships a rule
    Cisco ASA/FTD Buffer Overflow

Social

2026-10-21: 0 posts2026-10-22: 0 posts2026-10-23: 0 posts2026-10-24: 0 posts2026-10-25: 0 posts2026-10-26: 0 posts2026-10-27: 0 posts2026-10-28: 0 posts2026-10-29: 0 posts2026-10-30: 0 posts2026-10-31: 0 posts2026-11-01: 0 posts2026-11-02: 0 posts2026-11-03: 0 posts

No posts seen yet on X, Bluesky, Mastodon, Hacker News or GitHub.

Vendor statements

Quoted
CloudflareWAF Managed Rules3 quotesBlocks by default

First rule 2025-09-28, 3 days after the CVE was published.

2025-09-28New rule…9ee0ab84Default: DisabledSource
Cisco Secure Firewall Adaptive Security Appliance - Remote Code Execution - CVE:CVE-2025-20333, CVE:CVE-2025-20362, CVE:CVE-2025-20363. Previous action: N/A. New action: Disabled. This is a New Detection
2025-09-28New rule…d30f768eDefault: DisabledSource
Cisco Secure Firewall Adaptive Security Appliance - Remote Code Execution - CVE:CVE-2025-20333, CVE:CVE-2025-20362, CVE:CVE-2025-20363. Previous action: N/A. New action: Disabled. This is a New Detection
2025-10-07New rule…3a4d1bd6Default: BlockSource
Cisco Secure Firewall Adaptive Security Appliance - Remote Code Execution - CVE:CVE-2025-20333, CVE:CVE-2025-20362, CVE:CVE-2025-20363. Previous action: N/A. New action: Block. This is a New Detection
AWSAWS WAF Managed RulesNo public claim

We found no public statement from this vendor naming this CVE. That is not proof of no protection: generic rules may still catch it. AWS often describes a vulnerability without naming its CVE (for example "Log4j"). We count only entries that name the CVE, so AWS coverage is understated.

Microsoft AzureFront Door and Application Gateway WAF (DRS)No public claim

We found no public statement from this vendor naming this CVE. That is not proof of no protection: generic rules may still catch it. The rule tables name CVEs but carry no dates, so Azure is left out of every time-to-rule figure.

Google CloudCloud Armor preconfigured WAF rulesNo public claim

We found no public statement from this vendor naming this CVE. That is not proof of no protection: generic rules may still catch it. Google names few CVEs: the release notes start in May 2024 and the rules reference lists CVEs without dates. Its cve-canary rules are opt-in.

FastlyNext-Gen WAF virtual patchesBefore feed history

The CVE predates the oldest entry in this vendor's public feed, so a rule may exist that we cannot see.

F5Attack signatures (Distributed Cloud WAF)1 quoteRule published

First rule 2025-12-03, 69 days after the CVE was published.

2025-12-03New rule200011107Source
Added: signature 200011107 "Cisco ASA/FTD Buffer Overflow" (Buffer Overflow, risk High), systems: Cisco. References: CVE-2025-20333.
AkamaiApp & API Protector (Adaptive Security Engine)No public source

This vendor publishes no machine-readable rule changelog we can check.

OWASP CRSCore Rule Set (open source, used inside many WAFs)No public claim

We found no public statement from this vendor naming this CVE. That is not proof of no protection: generic rules may still catch it. CRS rarely names CVEs: it relies on generic detections. Our own lab measures what it actually blocks.