SSH daemon allocates unbounded idle session channels, bypassing max_channels
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.
CVE-2026-68956
Primary source · Revision 1
Imported from structured advisory data. Source references identify upstream records or fields; verify affected versions and your deployed configuration.
Security context
Source reference: cve:CVE-2026-68956
OTP
Source reference: /containers/cna/affected/0/product
- Affected versions
- Not stated in this record
- Fixed versions
- Not stated in this record
- Prerequisites
- Not stated in this record
OTP
Source reference: /containers/cna/affected/1/product
- Affected versions
- Not stated in this record
- Fixed versions
- Not stated in this record
- Prerequisites
- Not stated in this record
OTP
Source reference: /containers/cna/affected/2/product
- Affected versions
- Not stated in this record
- Fixed versions
- Not stated in this record
- Prerequisites
- Not stated in this record
Structured affected-version data
Original package identities and version rules from this source.
[
{
"cpes": [
"cpe:2.3:a:erlang:erlang\\/otp:*:*:*:*:*:*:*:*"
],
"vendor": "Erlang",
"modules": [
"ssh_connection",
"ssh_channel_sup"
],
"product": "OTP",
"versions": [
{
"status": "affected",
"changes": [
{
"at": "27.3.4.18",
"status": "unaffected"
},
{
"at": "28.5.0.7",
"status": "unaffected"
},
{
"at": "29.1.1",
"status": "unaffected"
}
],
"version": "18.1.2",
"lessThan": "*",
"versionType": "otp"
}
],
"packageURL": "pkg:software-id/erlang.org/otp",
"packageName": "otp",
"programFiles": [
"lib/ssh/src/ssh_connection.erl",
"lib/ssh/src/ssh_channel_sup.erl"
],
"defaultStatus": "unknown",
"programRoutines": [
{
"name": "ssh_connection:handle_msg/4"
},
{
"name": "ssh_connection:setup_session/5"
},
{
"name": "ssh_channel_sup:max_num_channels_not_exceeded/2"
}
]
},
{
"cpes": [
"cpe:2.3:a:erlang:erlang\\/otp:*:*:*:*:*:*:*:*"
],
"repo": "https://github.com/erlang/otp",
"vendor": "Erlang",
"modules": [
"ssh_connection",
"ssh_channel_sup"
],
"product": "OTP",
"versions": [
{
"status": "affected",
"changes": [
{
"at": "5.2.11.13",
"status": "unaffected"
},
{
"at": "5.5.2.6",
"status": "unaffected"
},
{
"at": "6.0.6",
"status": "unaffected"
}
],
"version": "4.1.1",
"lessThan": "*",
"versionType": "otp"
}
],
"packageURL": "pkg:otp/ssh",
"packageName": "ssh",
"programFiles": [
"src/ssh_connection.erl",
"src/ssh_channel_sup.erl"
],
"defaultStatus": "unknown",
"programRoutines": [
{
"name": "ssh_connection:handle_msg/4"
},
{
"name": "ssh_connection:setup_session/5"
},
{
"name": "ssh_channel_sup:max_num_channels_not_exceeded/2"
}
]
},
{
"cpes": [
"cpe:2.3:a:erlang:erlang\\/otp:*:*:*:*:*:*:*:*"
],
"repo": "https://github.com/erlang/otp",
"vendor": "Erlang",
"modules": [
"ssh_connection",
"ssh_channel_sup"
],
"product": "OTP",
"versions": [
{
"status": "affected",
"changes": [
{
"at": "79c2d2be17d902c5f53969b5806b725efda831be",
"status": "unaffected"
},
{
"at": "e18100975f0e5a8d59d02de00df12247a91b443b",
"status": "unaffected"
},
{
"at": "e2bbad0107bba41491a4d549686fd023db8740da",
"status": "unaffected"
}
],
"version": "84df3d4d0278e21a36a453bfee94799f0df67c2a",
"lessThan": "*",
"versionType": "git"
},
{
"status": "unaffected",
"version": "79c2d2be17d902c5f53969b5806b725efda831be",
"lessThan": "*",
"versionType": "git"
},
{
"status": "unaffected",
"version": "e18100975f0e5a8d59d02de00df12247a91b443b",
"lessThan": "*",
"versionType": "git"
},
{
"status": "unaffected",
"version": "e2bbad0107bba41491a4d549686fd023db8740da",
"lessThan": "*",
"versionType": "git"
}
],
"packageURL": "pkg:github/erlang/otp",
"packageName": "erlang/otp",
"programFiles": [
"lib/ssh/src/ssh_connection.erl",
"lib/ssh/src/ssh_channel_sup.erl"
],
"collectionURL": "https://github.com",
"defaultStatus": "unknown",
"programRoutines": [
{
"name": "ssh_connection:handle_msg/4"
},
{
"name": "ssh_connection:setup_session/5"
},
{
"name": "ssh_channel_sup:max_num_channels_not_exceeded/2"
}
]
}
]- Related CVEs
- CVE-2026-68956
Source reference:
/cveMetadata/cveId
Publisher severity
high
Source reference: /containers/cna/metrics
- Event
- #1882 · Revision 1
- Added to Heist Feed
- Publisher date