vulnerability / NVI-00014180 / Revision 2
JLine3 Telnet server: Unauthenticated Remote Memory Exhaustion via Unbounded Telnet NEW-ENVIRON Variables
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
0.592%
FIRST EPSS model v2026.06.15; exploitation probability over 30 days, percentile 0.48359. Missing scores are unknown.
As of · FIRST EPSS
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 limit the number of environment variables a client may inject via the Telnet NEW-ENVIRON option. An unauthenticated attacker can flood the server with a large number of unique variable pairs before sending the terminating IAC SE byte, exhausting JVM heap memory and causing an OutOfMemoryError (denial of service). Approximately 3–4 MB of network traffic is sufficient to consume a 512 MB JVM heap. ### Details `TelnetIO.readNEVariables()` (TelnetIO.java:1127-1180) processes incoming NEW-ENVIRON variable pairs in a loop and stores each pair in a `HashMap` held by `ConnectionData`: ```java // TelnetIO.java:1139-1178 boolean cont = true; if (i == NE_VAR || i == NE_USERVAR) { do { switch (readNEVariableName(sbuf)) { case NE_VAR_OK: TelnetIO.this.connectionData.getEnvironment().put(str, sbuf.toString()); // ← no per-connection count limit break; case NE_VAR_UNDEFINED: break; // cont remains true, loop continues } } while (cont); // cont is never set to false; only exits via return } ``` The variable accu
org.jline:jline-remote-telnet
source listed>= 4.0.0, < 4.0.16
### Summary The JLine3 Telnet server (`remote-telnet` module) does not limit the number of environment variables a client may inject via the Telnet NEW-ENVIRON option. An unauthenticated attacker can flood the server with a large number of unique variable pairs before sending the terminating IAC SE byte, exhausting JVM heap memory and causing an OutOfMemoryError (denial of service). Approximately 3–4 MB of network traffic is sufficient to consume a 512 MB JVM heap. ### Details `TelnetIO.readNEVariables()` (TelnetIO.java:1127-1180) processes incoming NEW-ENVIRON variable pairs in a loop and stores each pair in a `HashMap` held by `ConnectionData`: ```java // TelnetIO.java:1139-1178 boolean cont = true; if (i == NE_VAR || i == NE_USERVAR) { do { switch (readNEVariableName(sbuf)) { case NE_VAR_OK: TelnetIO.this.connectionData.getEnvironment().put(str, sbuf.toString()); // ← no per-connection count limit break; case NE_VAR_UNDEFINED: break; // cont remains true, loop continues } } while (cont); // cont is never set to false; only exits via return } ``` The variable accu
org.jline:jline-remote-telnet
source listed< 3.30.14
### Summary The JLine3 Telnet server (`remote-telnet` module) does not limit the number of environment variables a client may inject via the Telnet NEW-ENVIRON option. An unauthenticated attacker can flood the server with a large number of unique variable pairs before sending the terminating IAC SE byte, exhausting JVM heap memory and causing an OutOfMemoryError (denial of service). Approximately 3–4 MB of network traffic is sufficient to consume a 512 MB JVM heap. ### Details `TelnetIO.readNEVariables()` (TelnetIO.java:1127-1180) processes incoming NEW-ENVIRON variable pairs in a loop and stores each pair in a `HashMap` held by `ConnectionData`: ```java // TelnetIO.java:1139-1178 boolean cont = true; if (i == NE_VAR || i == NE_USERVAR) { do { switch (readNEVariableName(sbuf)) { case NE_VAR_OK: TelnetIO.this.connectionData.getEnvironment().put(str, sbuf.toString()); // ← no per-connection count limit break; case NE_VAR_UNDEFINED: break; // cont remains true, loop continues } } while (cont); // cont is never set to false; only exits via return } ``` The variable accu
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. FIRST EPSS
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-47qp-hqvx-6r3f ↗
GitHub Advisory Database · vendor advisory
Observed . GitHub Advisory Database; CC-BY-4.0. Each advisory links its original attribution. Null normalizes fields.
- CVE-2026-56740 ↗
FIRST EPSS · official catalog
Observed . FIRST EPSS; probability of exploitation in the next 30 days, not local compromise. Dataset date/model retained; FIRST services terms apply.
Public revision history
Only published revisions appear here. Routine fetches do not create a material-change event.
- Revision 2 ·
Dated EPSS estimate updated; this is not a new disclosure or proof of exploitation.
- Revision 1 ·
First indexed by Null; source disclosure date is shown separately.