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Attackers are exploiting a new critical zero-day flaw in Cisco Catalyst SD-WAN Manager, the system companies use to manage their Cisco SD-WAN networks, Cisco said in an advisory on September 30. The flaw, CVE-2026-76504, could allow a remote attacker with no login access to use the Manager's API as the admin user. Fixed releases are available, and there is no workaround. It carries a CVSS score of 9.8 out of 10. It sits in the part of the Manager's API that handles login sessions. The Manager mishandles URI encoding in an HTTP request. A crafted request can therefore bypass an authentication rule intended to restrict access to a single API endpoint. The attacker needs no credentials, only the ability to send that request to the Manager's API. Managers exposed to the internet are at risk of compromise, according to Cisco. By default, the admin user holds the netadmin role, which is allowed to perform all operations on the device. Cisco said its Product Security Incident Response Team "became aware of active exploitation of this vulnerability" in September 2026. The flaw was found while Cisco's Technical Assistance Center (TAC) was handling a support case. The advisory does not say how many customers were attacked, when the attacks began, who carried them out, or what the attackers did with the access. Who Needs to Upgrade The flaw affects SD-WAN Manager regardless of how the system is configured. No other product is listed as affected. These are the first fixed releases for each release train: CVE-2026-76504 is separate from three Cisco SD-WAN flaws fixed earlier: CVE-2026-20182 in May, and CVE-2026-20245 and CVE-2026-20262 in June. A comparison of the advisories shows that the fixed releases for those flaws are all older than the ones in the table above. So a Manager last upgraded for the May or June fixes still needs this update. The table does not list the 20.10, 20.11, 20.13, 20.14, or 20.16 release trains, which Cisco's May advisory did list. The advisory also does not name Cisco SD-WAN Cloud-Pro or Cisco SD-WAN for Government (FedRAMP), two deployment types named in the May and June advisories. Cisco SD-WAN Cloud (Cisco Managed) is already fixed in release 20.15.605, and customers on it need to take no action. Until an on-prem Manager is upgraded, Cisco advises restricting access to it from unsecured networks such as the internet. Where internet access is required, only known, trusted hosts should be allowed in, and the control components should sit behind a firewall. Cisco Catalyst SD-WAN Cloud Hosted environments already have this mitigation in place. The mitigation worked in a test environment, according to Cisco, which advises customers to assess its impact on their own networks before applying it. Cisco's SD-WAN hardening guide says administrative interfaces, such as ports 443, 22 and 830, should not be exposed directly to the internet. HTTPS access to the Manager should come only from a jump host or a management subnet. Checking for Signs of Compromise The signs of compromise Cisco describes involve j_security_check, the request path the Manager uses for session-based logins. In Cisco's example, one character of that path is URI-encoded, giving /%6a_security_check, where %6a stands for the letter j. Two log files are the places to look for j_security_check entries from unknown or unauthorized IP addresses: File: /var/log/nms/containers/service-proxy/serviceproxy-access.log File: /var/log/nms/vmanage-server.log, in particular entries for users whose names start with viptela-reserved- Names starting with viptela-reserved- belong to reserved system service accounts. Any one character in the request can be encoded, so %6a is only an example. The same entries can also appear during normal operation, and each match has to be checked against normal activity to avoid false positives. To help determine whether a Manager has been compromised, customers can open a Severity 3 case with Cisco TAC and include CVE-2026-76504 in the title. Cisco asks them to run request admin-tech on the Manager first, so the output file can be reviewed. The advisory includes no detection rule and does not say whether upgrading removes an attacker who already has access. Cisco's advisories for the May flaw and the first June flaw said an update alone would not resolve a confirmed compromise. They told customers to collect the admin-tech file before upgrading. CVE-2026-76504 follows a series of Cisco SD-WAN flaws flagged as exploited this year. As of September 30, the U.S. Cybersecurity and Infrastructure Security Agency's (CISA) Known Exploited Vulnerabilities catalog listed eight Cisco SD-WAN flaws added in 2026.

The U.S. Cybersecurity and Infrastructure Security Agency (CISA) on Friday added two security flaws impacting Microsoft SharePoint and Mikrotik RouterOS to its Known Exploited Vulnerabilities (KEV) catalog, citing evidence of active exploitation. The vulnerabilities in question are as follows - CVE-2026-65660 (CVSS score: 8.8) - A code injection vulnerability in Microsoft Office SharePoint that allows an authorized attacker to execute code over a network. CVE-2026-67279 (CVSS score: 6.9) - An improper enforcement of behavioral workflow vulnerability in Mikrotik RouterOS that could allow an unauthenticated client to open a session channel and send an exec request. As reported by The Hacker News earlier this week, CVE-2026-65660 was originally described by Microsoft as a spoofing vulnerability impacting SharePoint Server. The tech giant has since updated the advisory to state that it could be abused to obtain remote code execution. "As of 9/25/2026, Microsoft had reliable evidence of observed attacks against exploitation of this vulnerability," the Windows maker noted. Microsoft hasn't disclosed who was behind the exploitation efforts, when they started, how many organizations have been targeted, how many of them have been successful, and what attackers did once inside the vulnerable service. The second vulnerability to be added to the KEV catalog is CVE-2026-67279, which has been chained along with CVE-2026-86060, an argument injection flaw in the RouterOS login process, as part of an exploit codenamed MikroTrick. The exploit chain has been employed to take full administrative control of internet-exposed susceptible routers without the need for a password, per CERT Polska. "Combining the two vulnerabilities resulted in full unauthenticated access to the administrative console," the Polish cybersecurity agency said. "CVE-2026-67279 allowed an unauthenticated client to create a session channel, while CVE-2026-86060 allowed it to supply login with an attacker-controlled policy mask." In a separate analysis, Bishop Fox said it was able to reproduce the complete administrative takeover on vulnerable RouterOS 7.x builds. "MikroTrick combines two failures at different trust boundaries," security researcher Emilio Gallegos said. "The first allows an unauthenticated connection to reach functionality that RouterOS should expose only after login. The second causes the login process to treat data from that connection as a trusted administrative identity." "MikroTrick exposes a design risk in privileged software: a feature intended only for trusted local callers becomes a remote attack surface when an upstream component loses track of authentication state." It's worth noting that CISA added CVE-2026-86060 to its KEV catalog on September 11, 2026. Federal Civilian Executive Branch (FCEB) agencies have time until September 28, 2026, to apply the necessary fixes.