Last updated: September 29, 2026 at 8:42 AM UTC
All 891 Vulnerability 357 Breach 144 Threat 383 Defense 7
Tag: authentication-bypass (21 articles)Clear

Qilin ransomware crews break in through a Palo Alto VPN authentication bypass

Arctic Wolf Labs investigated multiple intrusions in June that began by exploiting an authentication bypass in Palo Alto Networks PAN-OS and ended in Qilin ransomware. CVE-2026-0257 affects the portal and gateway components and lets an unauthenticated remote attacker establish a VPN session without valid credentials, but only where authentication override cookies are enabled alongside specific certificate configurations. That narrow precondition makes it easy to assume you are unaffected without checking. The flaw is patched. Because it grants VPN access rather than code execution, the intrusions look like ordinary remote logins at the start, which delays detection until ransomware is deployed.

Check
Confirm PAN-OS is patched against this flaw and check whether authentication override cookies are enabled with the certificate configurations that make it exploitable, since the precondition is easy to overlook.
Affected
Organizations running unpatched PAN-OS portal or gateway components with authentication override cookies enabled (CVE-2026-0257); attackers establish VPN sessions without credentials, and Qilin affiliates have used this for initial access.
Fix
Patch PAN-OS, disable authentication override cookies where not required, require multi-factor authentication on VPN access, and hunt for VPN sessions lacking a corresponding authentication event or coming from unexpected locations.

Critical BeyondTrust flaws let attackers bypass authentication on remote-access appliances

BeyondTrust has patched two critical flaws in its Remote Support and Privileged Remote Access products that let an unauthenticated, network-positioned attacker bypass authentication and reach the appliance, including accounts with elevated privileges. The bugs, CVE-2026-40138 and CVE-2026-40139, both rated 9.2, sit in the authentication subsystem and depend on a specific authentication configuration being enabled. Cloud-hosted customers were patched automatically in April, but self-hosted deployments on version 25.3.2 or earlier need to update themselves. BeyondTrust has not reported exploitation, but its remote-support products have a history of being attacked, including flaws used to breach the US Treasury and to deploy ransomware, so internet-facing appliances should be patched quickly.

Check
Identify any self-hosted BeyondTrust Remote Support or Privileged Remote Access appliances, confirm their versions, prioritize internet-facing ones, and review whether the specific authentication configuration these flaws require is enabled.
Affected
Self-hosted BeyondTrust Remote Support and Privileged Remote Access appliances on version 25.3.2 or earlier (CVE-2026-40138, CVE-2026-40139); an unauthenticated attacker can bypass authentication and gain access, including to privileged accounts.
Fix
Apply the April security rollup or upgrade to Remote Support and Privileged Remote Access 25.3.3 or later, prioritize internet-facing appliances, and review authentication configurations and logs for unauthorized access.

Gitea Docker images trusted a forged header, letting anyone log in as any user

Attackers have started probing a critical flaw in Gitea's official Docker images, the self-hosted Git service used by many development teams. The images shipped a configuration that trusted the X-WEBAUTH-USER header from any source address, so with reverse-proxy login enabled, anyone who could reach the port could send that header and be authenticated as any user, no password required. Tracked as CVE-2026-20896 and rated 9.8, it was fixed in version 1.26.3 late last month, which removes the wildcard and makes reverse-proxy authentication opt-in. Sysdig reported the first exploitation attempt 13 days after disclosure, so far just reconnaissance, against some of the roughly 6,200 internet-facing Gitea instances.

Check
Check whether you run Gitea from its Docker image and on what version, review the app.ini reverse-proxy trusted-proxies setting for a wildcard, and whether the instance is internet-reachable.
Affected
Self-hosted Gitea Docker deployments on version 1.26.2 or earlier with reverse-proxy login enabled (CVE-2026-20896); an unauthenticated attacker who can reach the service can impersonate any user by forging one header.
Fix
Update Gitea to 1.26.3 or later, remove the wildcard from the reverse-proxy trusted-proxies setting, keep management interfaces off the public internet, and review logs for spoofed X-WEBAUTH-USER authentication attempts.

Curl's largest security release fixes 18 flaws, including a 25-year-old bug

The curl project shipped its largest-ever security release, version 8.21.0, fixing 18 vulnerabilities, among them a flaw that had gone unnoticed for 25 years. That bug (CVE-2026-8932) lets an application reuse an existing connection even after its client certificate or key changed, allowing an authentication bypass; it affects software built on the libcurl library rather than the command-line tool. Other fixes address credential confusion, memory-corruption bugs, and improper host validation. Most are rated medium or low, but libcurl is embedded in an enormous range of products, from IoT devices to CI/CD pipelines and cars, so the practical reach is large and easy to overlook.

Check
Identify where curl and especially the libcurl library are used across your applications, devices, containers, and build pipelines, since most exposure comes from embedded libcurl rather than the command-line tool.
Affected
Applications and devices built on libcurl before version 8.21.0 (CVE-2026-8932 and others); those using mutual TLS with changing client certificates face an authentication-bypass risk through connection reuse.
Fix
Update to curl and libcurl 8.21.0, rebuild and redeploy software that bundles libcurl, and prioritize systems using mutual TLS or handling credentials, including embedded and IoT devices that update slowly.

One unpatched Quest KACE box at a Boston MSP exposed 60+ named client organizations - law enforcement, schools, healthcare, and government on one MariaDB dump (CVE-2025-32975)

Quest KACE has a year-old maximum-severity authentication bypass (CVE-2025-32975, CVSS 10.0). Hunt.io researchers now report that an attacker exploited an unpatched KACE appliance at a Boston-area managed services provider called HIQ - then left their entire toolkit on a publicly accessible server with directory listing turned on. The exfiltrated 512 MB MariaDB dump turned out to contain the full appliance-managed endpoint list for over 60 named client organizations spanning law enforcement, government, healthcare, education, and private companies. None of those 60-plus organizations had any KACE relationship of their own - they were just customers of the MSP that ran it unpatched.

Check
Inventory Quest KACE SMA instances reachable from the public internet, check their version against the May 2025 patched build, and review helpdesk tickets and asset records for sensitive material that would surface in a database dump.
Affected
Quest KACE Systems Management Appliance (SMA) instances at or below the pre-May 2025 patched version. CVSS 10.0 unauthenticated SSO impersonation. CISA KEV-listed since April 2026.
Fix
Apply Quest's May 2025 patched version immediately. Remove KACE SMA from direct internet exposure (place behind VPN or firewall), rotate KACE admin credentials, and audit for unauthorized accounts created via runkbot.exe.

Critical MOVEit Automation flaw lets attackers take over file-transfer servers without logging in - Cl0p hit MOVEit's sister product in 2023 and stole data from 62 million people (CVE-2026-4670)

Progress Software released emergency patches Sunday for two MOVEit Automation flaws. The worst, CVE-2026-4670 (CVSS 9.8), lets remote attackers reach the management interface without logging in - and from there take administrative control. Airbus researchers disclosed both flaws privately and Progress hasn't seen exploitation in the wild, but the comparison with MOVEit's history is uncomfortable: the Cl0p ransomware gang exploited MOVEit Transfer in 2023 to steal data from 2,100 organizations and 62 million individuals. Shodan shows 1,400+ MOVEit Automation instances exposed online, including a dozen linked to US local and state government agencies.

Check
Inventory MOVEit Automation instances and check the version under Web Admin > Help > About. Search firewall logs for inbound traffic to the service backend command port.
Affected
MOVEit Automation versions before 2025.1.5, 2025.0.9, and 2024.1.8. CVE-2026-4670 (CVSS 9.8, auth bypass) and CVE-2026-5174 (CVSS 7.7, privilege escalation). 1,400+ internet-exposed instances per Shodan, including state and local government agencies. Internet-reachable management interfaces face acute risk.
Fix
Upgrade to MOVEit Automation 2025.1.5, 2025.0.9, or 2024.1.8 using the full installer (the standard service installer does not patch the flaw). Restrict the management interface to internal networks only. Rotate every credential MOVEit holds for downstream destinations - cloud storage, SFTP servers, partner systems. Block external traffic to the service backend command port at the firewall.

SonicWall patches three SonicOS firewall flaws after CrowdStrike disclosed them - the worst lets attackers reach the management interface without logging in (CVE-2026-0204)

SonicWall released emergency firmware updates for Gen 6, Gen 7, and Gen 8 firewalls after CrowdStrike's research team disclosed three SonicOS flaws on April 29. The worst is CVE-2026-0204 (CVSS 8.0), a weak authentication bug in the management interface that lets an attacker on an adjacent network reach management functions without logging in - and from there change firewall rules, disable security protections, or open new holes. The other two are post-authentication: CVE-2026-0205 is a path traversal that breaks out of restricted directories, and CVE-2026-0206 is a buffer overflow that crashes the firewall. No public exploits yet.

Check
Patch every SonicWall Gen 6, Gen 7, and Gen 8 firewall to the latest firmware today, and confirm no SonicWall management interface or SSL-VPN is reachable from the public internet.
Affected
Gen 6 firewalls (TZ 300/400/500/600, NSA, SM, SOHO) running 6.5.5.1-6n or older. Gen 7 firewalls and NSv (TZ270-TZ670, NSa 2700-6700, NSsp, NSv on ESX/KVM/Hyper-V/AWS/Azure) running 7.0.1-5169 or 7.3.1-7013 or older. Gen 8 (TZ80-TZ680, NSa 2800-5800) running 8.1.0-8017 or older.
Fix
Upgrade to Gen 8 firmware 8.2.0-8009, Gen 7 firmware 7.3.2-7010, or Gen 6 6.5.5.2-28n. Until patched, disable HTTP and HTTPS firewall management on all interfaces, disable SSL-VPN, and restrict management to SSH only from trusted IPs. Take a full configuration backup before upgrading Gen 6 - downgrading from 6.5.5.2-28n deletes all LDAP users and resets MFA.

All cPanel and WHM versions had a critical authentication bypass that attackers may have been exploiting since February - emergency patches now released (CVE-2026-41940)

cPanel disclosed a critical authentication bypass on Monday affecting every cPanel and WHM version - including end-of-life builds. CVSS 9.8. The bug let unauthenticated attackers log in as administrators by abusing how the cPanel session daemon writes session files during login. Hosting providers including Namecheap, KnownHost, hosting.com, HostPapa, and InMotion took cPanel and WHM offline globally for hours while patches deployed. Researchers at watchTowr published a working proof-of-concept on April 29. KnownHost reports possible targeted exploitation as early as February 23, 2026 - more than two months before disclosure.

Check
If you run any cPanel or WHM server, confirm it's patched to 11.110.0.97, 11.118.0.63, 11.126.0.54, 11.132.0.29, 11.134.0.20, or 11.136.0.5 today.
Affected
All cPanel and WHM versions before the April 28 emergency patch, plus end-of-life versions. CVE-2026-41940, CVSS 9.8. Successful exploitation grants root-equivalent access on the server, exposing every hosted website, database, email account, and customer data. KnownHost reports possible exploitation since February 23, 2026.
Fix
Run '/scripts/upcp --force' to pull the latest patched cPanel build immediately. Audit authentication logs for unusual successful logins between February 23 and April 28 - any login from an unfamiliar IP during that window may indicate prior compromise. Block cPanel ports (2082-2087, 2095-2096, 2077-2078) at the firewall to non-trusted IP ranges.

Microsoft ships emergency out-of-band patch for critical ASP.NET Core authentication cookie forgery flaw (CVE-2026-40372)

Microsoft released out-of-band security updates for a critical ASP.NET Core Data Protection flaw that lets unauthenticated attackers forge authentication cookies and escalate to SYSTEM privileges. The bug (CVE-2026-40372) is a regression introduced in the April 2026 Patch Tuesday: the Microsoft.AspNetCore.DataProtection 10.0.0 through 10.0.6 NuGet packages compute the HMAC validation tag (the cryptographic signature that proves a cookie has not been tampered with) over the wrong bytes of the payload and then discard the hash in some cases. The broken check means attackers can forge payloads that pass DataProtection's authenticity checks and decrypt previously-protected data in auth cookies, antiforgery tokens, TempData, and OIDC state. Microsoft noticed the flaw only after users reported decryption failures in their apps after installing the .NET 10.0.6 update. Critical operational detail: updating to 10.0.7 stops future forgeries, but any tokens an attacker already got the app to legitimately sign during the vulnerable window (session refresh tokens, API keys, password reset links) remain valid forever unless you rotate the DataProtection key ring. Patching alone is not enough.

Check
Check whether any ASP.NET Core application you run is on the Microsoft.AspNetCore.DataProtection NuGet package versions 10.0.0 through 10.0.6.
Affected
Microsoft.AspNetCore.DataProtection NuGet package versions 10.0.0 through 10.0.6 (shipped as part of .NET 10.0.0 through .NET 10.0.6).
Fix
Update the Microsoft.AspNetCore.DataProtection package to 10.0.7 and redeploy. Critically, also rotate the DataProtection key ring after patching - any legitimately-signed tokens (session refresh, API keys, password reset links) issued to an attacker during the vulnerable window remain valid until the key ring is rotated. Audit auth logs from April 14 through April 22 for suspicious token issuance.

Nginx UI authentication bypass actively exploited - one unauthenticated request gives attackers full server takeover via MCP endpoint (CVE-2026-33032)

A CVSS 9.8 authentication bypass in nginx-ui, the popular open-source web management interface for Nginx servers, is being actively exploited in the wild. The flaw, codenamed MCPwn by Pluto Security, exists because the /mcp_message endpoint added for Model Context Protocol (AI integration) support only checks IP whitelisting - and the default whitelist is empty, meaning it allows all connections. One unauthenticated HTTP POST request lets an attacker invoke all MCP tools: rewrite Nginx config files, reload the server, intercept all traffic, and harvest admin credentials. Attackers chain it with CVE-2026-27944 (exposed encryption keys via the backup API) to extract the node_secret needed for full MCP access. Recorded Future flagged active exploitation and assigned a risk score of 94/100. Shodan shows 2,600 publicly exposed instances, mostly in China, the US, Indonesia, and Germany. Pluto Security's key lesson: AI integration endpoints expose the same capabilities as the core application but often skip its security controls.

Check
Check if you or any managed clients run nginx-ui (web-based Nginx management dashboard). If MCP support is enabled, this is urgent - you're likely exposed.
Affected
nginx-ui versions 2.3.5 and earlier with MCP support enabled. The tool has 11,000+ GitHub stars and 430,000 Docker pulls. Any instance reachable from the network is exploitable without credentials.
Fix
Update nginx-ui to version 2.3.6 immediately (2.3.4 was the first fix, 2.3.6 is current). If you can't patch: restrict network access to the nginx-ui management interface to trusted IPs only. Add authentication middleware to the /mcp_message endpoint. As defense-in-depth, audit all MCP-integrated tools in your environment - this class of flaw (AI integration endpoints skipping auth) will appear in other products.