CVE-2026-68956 SSH daemon allocates unbounded idle session channels, bypassing max_channels
An authenticated attacker can exhaust node memory by opening unbounded idle SSH session channels, causing a denial of service.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-68956?
CVE-2026-68956 is a high-severity denial of service vulnerability in Erlang OTP, published on 22 Sep 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Official description
Allocation of Resources Without Limits or Throttling vulnerability in Erlang/OTP ssh allows an authenticated remote attacker to exhaust node memory by repeatedly opening session channels that are never assigned a handler.
The "session" clause of ssh_connection:handle_msg/4 checks only minimal_remote_max_packet_size before calling setup_session/5, which unconditionally builds a #channel{} record and stores it in the ETS channel cache. The max_channels daemon option is consulted only by ssh_channel_sup:max_num_channels_not_exceeded/2, which counts supervisor children, so a channel that never gets a shell, exec, or subsystem handler is invisible to the limit and setting the option to a finite value does not mitigate the attack. RFC 4254 section 5.1 permits many session channels per connection, and each record costs only a few hundred bytes, so a single authenticated connection can accumulate channels until the node runs out of memory and the emulator terminates, affecting every application on it. No file contents, credentials, or write access are obtainable.
This issue affects OTP from OTP 18.1.2 before OTP 27.3.4.18, OTP 28.5.0.7, and OTP 29.1.1, corresponding to ssh from 4.1.1 before 5.2.11.13, 5.5.2.6, and 6.0.6. Whether OTP before OTP 18.1.2, corresponding to ssh before 4.1.1, is affected is unknown.
Weakness: CWE-770
Which versions are affected by CVE-2026-68956?
How do I fix CVE-2026-68956?
Upgrade to a fixed version.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-68956 being exploited?
There is no known exploitation of CVE-2026-68956 in the wild and no public exploit code.
Sources
Also known as AZL-103425, DEBIAN-CVE-2026-68956, EEF-CVE-2026-68956, GHSA-qhcm-px9c-rvfh, UBUNTU-CVE-2026-68956.