CVE-2026-55977 Overview
CVE-2026-55977 is a rate-limiting bypass vulnerability that allows an attacker with local network access to brute-force a screen-sharing code. Successful exploitation enables the attacker to join a screen-sharing session and potentially display harmful content on the affected screen. The weakness is classified under CWE-307: Improper Restriction of Excessive Authentication Attempts.
The issue was published to the National Vulnerability Database on 2026-07-28 and referenced by the Cyber Security Agency of Singapore in CSA Security Alert AL-2026-093.
Critical Impact
An adjacent-network attacker can bypass authentication throttling and guess valid screen-sharing codes, hijacking the display output of a targeted session.
Affected Products
- Product details were not published in the NVD record at the time of writing
- Refer to CSA Security Alert AL-2026-093 for vendor and version specifics
- Applies to screen-sharing functionality reachable over the local network
Discovery Timeline
- 2026-07-28 - CVE-2026-55977 published to NVD
- 2026-07-30 - Last updated in NVD database
Technical Details for CVE-2026-55977
Vulnerability Analysis
The vulnerability stems from insufficient throttling on the screen-sharing code verification endpoint. Screen-sharing sessions are typically protected by a short numeric or alphanumeric code. When the application fails to enforce rate limits, attempt counters, or lockout thresholds, an attacker can iterate through the entire code space in a short time. Local network access is sufficient because the affected verification path is reachable without traversing the public internet.
Once the attacker submits the correct code, the application accepts the session as legitimate. The attacker can then push arbitrary content onto the shared display, which can be used for harassment, disinformation, or social-engineering payloads targeting anyone viewing the screen.
Root Cause
The root cause is [CWE-307]: the application does not restrict the number of failed authentication attempts against the screen-sharing code. Absent controls include per-IP request throttling, exponential back-off, temporary account lockout, and code rotation after repeated failures.
Attack Vector
The attack vector is Local, requiring low privileges and no user interaction. The attacker must reach the screen-sharing service on the local network segment. From there, the attacker submits high-volume code guesses until one succeeds. No memory corruption, credential theft, or supply-chain access is required.
No public proof-of-concept exploit code has been released for CVE-2026-55977. Refer to the CSA advisory for technical details from the vendor.
Detection Methods for CVE-2026-55977
Indicators of Compromise
- High-frequency requests to the screen-sharing pairing or join endpoint from a single local host
- Repeated failed code-validation events in application logs preceding a successful join
- Screen-sharing sessions initiated from unexpected internal IP addresses or MAC addresses
- Unrecognized content briefly displayed on presentation or conference-room devices
Detection Strategies
- Baseline the normal rate of screen-sharing join attempts per source and alert on statistical deviations
- Correlate a burst of failed pairing attempts followed by a successful join within a narrow time window
- Inspect network flows for repeated small POST or WebSocket messages to the pairing service from one endpoint
Monitoring Recommendations
- Forward application and network telemetry from screen-sharing appliances into a central SIEM for correlation
- Enable verbose logging on the code-validation function, including source IP, timestamp, and outcome
- Track session-establishment events and alert on sessions that begin outside business hours or from atypical subnets
How to Mitigate CVE-2026-55977
Immediate Actions Required
- Apply the vendor patch referenced in CSA Security Alert AL-2026-093 as soon as it is available for your deployment
- Restrict access to the screen-sharing service to trusted VLANs or management subnets
- Increase the length and entropy of screen-sharing codes where the vendor supports configuration
- Rotate active session codes and terminate long-running sessions
Patch Information
Consult the CSA advisory for the affected vendor's fixed release. The advisory is the authoritative source for patched version numbers tied to CVE-2026-55977.
Workarounds
- Segment screen-sharing devices onto a dedicated network with strict access-control lists
- Disable remote code-based joining when in-person or credentialed joining is available
- Reduce the validity window of generated codes so brute-force attempts expire before completion
- Monitor for and manually block hosts that generate excessive failed pairing requests
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
