Analysis Summary

Cisco has disclosed a medium-severity vulnerability (CVE-2025-20255) affecting its cloud-based Webex Meetings service. The flaw, discovered by a security researcher, involves improper handling of malicious HTTP requests within the client join services component. This vulnerability enables remote, unauthenticated attackers to exploit HTTP cache behavior and serve manipulated content to unsuspecting Webex users. It has been assigned a CVSS score of Medium, indicating moderate risk. Cisco has already remediated the issue on its cloud platform, with no required action for customers.

The root cause of the vulnerability lies in the manipulation of unkeyed inputs in HTTP requests. Caches typically identify responses based on cache keys, ignoring other request components (unkeyed inputs). When unkeyed inputs influence the generated response without being considered in caching decisions, attackers can inject harmful payloads that get stored and served from cache to multiple users. This form of HTTP cache poisoning allows an attacker to poison the cache with a crafted response, which can then be served to any user who accesses the affected resource while the poisoned cache is active.

Unlike traditional attacks like cross-site scripting that target individual users, HTTP cache poisoning leverages shared infrastructure to amplify the impact. In this case, no authentication is required (AV:N), the attack has low complexity (AC:L), and requires limited user interaction (UI:R) — making it relatively accessible for attackers. While it only affects data integrity (I:L) and not confidentiality or availability, the potential consequences include session disruption or more severe outcomes if chained with other vulnerabilities. The vulnerability is categorized under CWE-349, which relates to improper validation of the cache key.

Cisco’s Product Security Incident Response Team (PSIRT) confirmed that no public exploitation was observed at the time of disclosure, and the vulnerability is now patched in the Webex cloud environment. Organizations using Webex do not need to take any corrective actions. Nonetheless, security professionals recommend proactive defenses against cache poisoning: validating and sanitizing all user inputs (especially HTTP headers), correctly configuring cache behaviors, and using response headers such as Vary to ensure appropriate caching decisions. These practices can help minimize exposure to similar threats across other web applications.

Impact

• Security Bypass
• Gain Access

Indicators of Compromise

CVE

• CVE-2025-20255

Affected Vendors

Remediation

• Refer to Cisco Security Advisory for patch, upgrade or suggested workaround information.
• Validate and sanitize all user inputs, especially HTTP headers.
• Ensure proper configuration of cache settings and behavior.
• Use response headers like Vary to control and isolate cache entries.
• Regularly audit and monitor caching mechanisms for anomalies.
• Keep all services and platforms up to date with the latest security patches.