vulnerability / NVI-00014073 / Revision 1
JLine3 Telnet server: Unauthenticated Remote DoS via Unbounded Telnet NAWS Terminal Geometry
GitHub lists this reviewed advisory for org.jline:jline-remote-telnet, org.jline:jline-remote-telnet, org.jline:jline-remote-telnet. Published version ranges and source prerequisites are shown below; this is not an inspection of a visitor’s application.
This report has not inspected your inventory, configuration, deployed build, reachability or evidence. A catalog listing and a severity score do not establish exposure or compromise.
01 / Meaning
Why it matters
Published affected context helps an owner decide what evidence to gather. This report has not examined your application.
7.5 high
GitHub source severity; exploitability and local consequence require separate evidence.
As of · GitHub Advisory Database
02 / Applicability
The affected context
Affected versions, configuration prerequisites and known exclusions are public. Confirm each one against the deployed service.
org.jline:jline-remote-telnet
source listed>= 4.1.0, < 4.2.1
### Summary The JLine3 Telnet server (`remote-telnet` module) does not apply an upper bound to terminal dimensions received via the Telnet NAWS (Negotiate About Window Size) option. An unauthenticated remote attacker can send a NAWS subnegotiation advertising a 65535×65535 terminal and repeatedly alternate values to trigger continuous, expensive rendering work on the server, causing CPU exhaustion and denial of service. ### Details `TelnetIO.handleNAWS()` (TelnetIO.java:856-879) reads the client-supplied width and height as 16-bit unsigned integers and passes them to `setTerminalGeometry()`: ```java // TelnetIO.java:869-875 private void setTerminalGeometry(int columns, int rows) { if (columns < SMALLEST_BELIEVABLE_WIDTH) columns = DEFAULT_WIDTH; // lower bound only if (rows < SMALLEST_BELIEVABLE_HEIGHT) rows = DEFAULT_HEIGHT; connectionData.setTerminalGeometry(columns, rows); connection.processConnectionEvent( new ConnectionEvent(connection, ConnectionEvent.Type.CONNECTION_TERMINAL_GEOMETRY_CHANGED)); } ``` Only a *lower* bound is enforced (minimum 20 columns / 6 rows). Values up to 65535 are accepted and stored. The geometry change event propaga
org.jline:jline-remote-telnet
source listed>= 4.0.0, < 4.0.16
### Summary The JLine3 Telnet server (`remote-telnet` module) does not apply an upper bound to terminal dimensions received via the Telnet NAWS (Negotiate About Window Size) option. An unauthenticated remote attacker can send a NAWS subnegotiation advertising a 65535×65535 terminal and repeatedly alternate values to trigger continuous, expensive rendering work on the server, causing CPU exhaustion and denial of service. ### Details `TelnetIO.handleNAWS()` (TelnetIO.java:856-879) reads the client-supplied width and height as 16-bit unsigned integers and passes them to `setTerminalGeometry()`: ```java // TelnetIO.java:869-875 private void setTerminalGeometry(int columns, int rows) { if (columns < SMALLEST_BELIEVABLE_WIDTH) columns = DEFAULT_WIDTH; // lower bound only if (rows < SMALLEST_BELIEVABLE_HEIGHT) rows = DEFAULT_HEIGHT; connectionData.setTerminalGeometry(columns, rows); connection.processConnectionEvent( new ConnectionEvent(connection, ConnectionEvent.Type.CONNECTION_TERMINAL_GEOMETRY_CHANGED)); } ``` Only a *lower* bound is enforced (minimum 20 columns / 6 rows). Values up to 65535 are accepted and stored. The geometry change event propaga
org.jline:jline-remote-telnet
source listed< 3.30.14
### Summary The JLine3 Telnet server (`remote-telnet` module) does not apply an upper bound to terminal dimensions received via the Telnet NAWS (Negotiate About Window Size) option. An unauthenticated remote attacker can send a NAWS subnegotiation advertising a 65535×65535 terminal and repeatedly alternate values to trigger continuous, expensive rendering work on the server, causing CPU exhaustion and denial of service. ### Details `TelnetIO.handleNAWS()` (TelnetIO.java:856-879) reads the client-supplied width and height as 16-bit unsigned integers and passes them to `setTerminalGeometry()`: ```java // TelnetIO.java:869-875 private void setTerminalGeometry(int columns, int rows) { if (columns < SMALLEST_BELIEVABLE_WIDTH) columns = DEFAULT_WIDTH; // lower bound only if (rows < SMALLEST_BELIEVABLE_HEIGHT) rows = DEFAULT_HEIGHT; connectionData.setTerminalGeometry(columns, rows); connection.processConnectionEvent( new ConnectionEvent(connection, ConnectionEvent.Type.CONNECTION_TERMINAL_GEOMETRY_CHANGED)); } ``` Only a *lower* bound is enforced (minimum 20 columns / 6 rows). Values up to 65535 are accepted and stored. The geometry change event propaga
03 / Response
What to do next
- investigate
Identify the exact component and deployed version, examine the linked publisher’s conditions, and retain evidence of any mitigation.
Confirm current vendor support, compatibility and deployment evidence. This report has not tested a fix in your system. GitHub Advisory Database
A fixed release is not deployment evidence.
Check current vendor support and compatibility. After making a change, verify the deployed build and relevant runtime conditions. Keep the evidence, owner and time. An updated lockfile alone does not prove what is running.
04 / Limits
What this report cannot establish
- Customer inventory, deployment, reachability and exploitation have not been inspected.
05 / Provenance
Sources you can inspect
Each assertion retains its source. Mirrored records may repeat one underlying publisher; additional links are not independent corroboration.
- GHSA-2r2c-cx56-8933 ↗
GitHub Advisory Database · vendor advisory
Observed . GitHub Advisory Database; CC-BY-4.0. Each advisory links its original attribution. Null normalizes fields.
Public revision history
Only published revisions appear here. Routine fetches do not create a material-change event.
- Revision 1 ·
First indexed by Null; source disclosure date is shown separately.