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Versa Concerto Authentication Bypass File Write Remote Code Execution

Not in CISA KEVCVE-2025-34027CWE-367

Not confirmed exploited. 2 of 8 rule sources name it; Cloudflare blocks by default. Our CRS test: not blocked.

Edge rules
2/8
Our test
Not blocked
CVSS
10.0
EPSS
46.4% Top 1%
Posts, 14d
02026-10-21: 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
Published
2025-05-21
The Versa Concerto SD-WAN orchestration platform is vulnerable to an authentication bypass in the Traefik reverse proxy configuration, allowing at attacker to access administrative endpoints. The Spack upload endpoint can be leveraged for… More

The Versa Concerto SD-WAN orchestration platform is vulnerable to an authentication bypass in the Traefik reverse proxy configuration, allowing at attacker to access administrative endpoints. The Spack upload endpoint can be leveraged for a Time-of-Check to Time-of-Use (TOCTOU) write in combination with a race condition to achieve remote code execution via path loading manipulation, allowing an unauthenticated actor to achieve remote code execution (RCE).This issue is known to affect Concerto from 12.1.2 through 12.2.0. Additional versions may be vulnerable.

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Ask about CVE-2025-34027: who's covered, what to patch first, how vendors compare. I cite sources and won't help with attacks.

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Severity, decoded

CVSS 4.0
Critical · 10.0 / 10

Exploitable over the network, with no privileges and no user interaction, leading to full loss of confidentiality and integrity and low impact on availability; other systems can also be hit (full loss of confidentiality and integrity and low impact on availability).

Over the internetNo login neededNo user actionWorks reliablySpreads beyond the appSerious impact
How the score is built11 metrics
  • Attack vectorAn attacker can reach it over the internet; no access to your network needed.
    Network
  • Attack complexityNo built-in defences have to be bypassed; the attack works reliably.
    Low
  • Attack requirementsThe attack works without any special deployment or timing conditions.
    None
  • Privileges requiredNo account or login is needed.
    None
  • User interactionNo one has to click or open anything; the attack works on its own.
    None
  • Confidentiality impact (vulnerable system)An attacker can read all data the affected component holds, or the most sensitive parts of it.
    High
  • Integrity impact (vulnerable system)An attacker can change any data or files the affected component protects.
    High
  • Availability impact (vulnerable system)An attacker can slow the component down or interrupt it now and then.
    Low
  • Confidentiality impact (other systems)Other systems that rely on it can have all their data read.
    High
  • Integrity impact (other systems)Other systems that rely on it can have any data changed.
    High
  • Availability impact (other systems)Other systems that rely on it can be slowed down or interrupted.
    Low
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:L/SC:H/SI:H/SA:L
CISA's assessmentSSVC, from the CVE record
ExploitationNone

CISA has seen no public exploit and no attacks.

AutomatableYes

Attackers can script the attack end to end and hit many targets at once.

Technical impactTotal

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

Public exploits

1 found
0 Metasploit0 Exploit-DB1 Scanner template0 GitHub PoCs

Links are to third-party code: never run it outside an isolated lab.

Timeline

  1. 2025-05-21
    CVE published
    CVE List
  2. 2025-06-02
    Cloudflare ships a rule
    Versa Concerto SD-WAN - Auth Bypass - CVE:CVE-2025-34027
  3. 2025-08-15
    F5 ships a rule
    Versa Concerto Authentication Bypass
  4. 2026-11-02
    Our test: OWASP Core Rule Set let it through
    paranoia level 1, anomaly threshold 5, default CRS settings
  5. 2026-11-02
    Our test: OWASP Core Rule Set let it through
    paranoia level 2, anomaly threshold 5, default CRS settings

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 Rules1 quoteBlocks by default

First rule 2025-06-02, 12 days after the CVE was published.

2025-06-02New rule…39b52f02Default: BlockSource
Versa Concerto SD-WAN - Auth Bypass - CVE:CVE-2025-34027. Previous action: Log. 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 2025-08-15, 86 days after the CVE was published.

2025-08-15New rule200013125Source
Added: signature 200013125 "Versa Concerto Authentication Bypass" (Authentication/Authorization Attacks, risk High), systems: Other Web Server. References: CVE-2025-34027.
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.