CVE-2026-54886 (GCVE-0-2026-54886)
Vulnerability from cvelistv5
Published
2026-07-02 16:06
Modified
2026-07-24 14:14
Severity ?
VLAI Severity ?
EPSS score ?
CWE
Summary
Loop with Unreachable Exit Condition ('Infinite Loop') vulnerability in Erlang OTP ssh (ssh_sftpd module) allows an authenticated SFTP user to render an SFTP channel permanently unresponsive.
The handle_data/4 function in ssh_sftpd contains a catch-all clause that accepts channel data of any type. When channel data with a non-zero type code (SSH_MSG_CHANNEL_EXTENDED_DATA) arrives with an empty pending buffer and a payload at or below the SFTP packet size limit, the clause tail-calls itself with identical arguments, creating an infinite loop.
The SFTP protocol operates exclusively on normal channel data (type 0). Extended data (non-zero type) is meaningless for SFTP and is never sent by conforming clients. However, the SSH protocol permits any channel participant to send extended data on an open channel, so an authenticated SFTP client can trigger the loop by sending SSH_MSG_CHANNEL_EXTENDED_DATA with any data_type_code and any non-empty payload at or below the size limit.
The targeted ssh_sftpd process enters an infinite tail-recursive loop. It never processes another message, its message queue grows without bound, and it can only be stopped by killing the process. BEAM's reduction-based scheduler preemption continues to function, so other processes on the node are not starved, but each stuck channel process consumes its full CPU time share continuously and accumulates unbounded message queue memory. Opening many channels amplifies the CPU and memory impact.
Erlang/OTP SSH configurations using the default max_channels setting (infinity) allow an authenticated user to open unlimited channels per connection, amplifying the attack without requiring multiple TCP connections or authentications.
No file contents, credentials, or write access are obtainable through this issue. The impact is limited to denial of service on targeted SFTP channels, with secondary CPU degradation and memory growth.
This vulnerability is associated with program file lib/ssh/src/ssh_sftpd.erl and program routine ssh_sftpd:handle_data/4.
This issue affects OTP from OTP 17.0 before OTP 29.0.3, OTP 28.5.0.3 and OTP 27.3.4.14, corresponding to ssh from 3.0.1 before 6.0.2, 5.5.2.2 and 5.2.11.9.
References
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|---|---|---|
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Impacted products
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The impact is limited to denial of service on targeted SFTP channels, with secondary CPU degradation and memory growth.\\n\\nThis vulnerability is associated with program file lib/ssh/src/ssh_sftpd.erl and program routine ssh_sftpd:handle_data/4.\\n\\nThis issue affects OTP from OTP 17.0 before OTP\\u00a029.0.3, OTP\\u00a028.5.0.3 and OTP\\u00a027.3.4.14, corresponding to ssh from 3.0.1 before 6.0.2, 5.5.2.2 and 5.2.11.9.\", \"supportingMedia\": [{\"type\": \"text/html\", \"value\": \"Loop with Unreachable Exit Condition (\u0027Infinite Loop\u0027) vulnerability in Erlang OTP \u003ctt\u003essh\u003c/tt\u003e (\u003ctt\u003essh_sftpd\u003c/tt\u003e module) allows an authenticated SFTP user to render an SFTP channel permanently unresponsive.\u003cp\u003eThe \u003ctt\u003ehandle_data/4\u003c/tt\u003e function in \u003ctt\u003essh_sftpd\u003c/tt\u003e contains a catch-all clause that accepts channel data of any type. When channel data with a non-zero type code (\u003ctt\u003eSSH_MSG_CHANNEL_EXTENDED_DATA\u003c/tt\u003e) arrives with an empty pending buffer and a payload at or below the SFTP packet size limit, the clause tail-calls itself with identical arguments, creating an infinite loop.\u003c/p\u003e\u003cp\u003eThe SFTP protocol operates exclusively on normal channel data (type 0). Extended data (non-zero type) is meaningless for SFTP and is never sent by conforming clients. However, the SSH protocol permits any channel participant to send extended data on an open channel, so an authenticated SFTP client can trigger the loop by sending \u003ctt\u003eSSH_MSG_CHANNEL_EXTENDED_DATA\u003c/tt\u003e with any \u003ctt\u003edata_type_code\u003c/tt\u003e and any non-empty payload at or below the size limit.\u003c/p\u003e\u003cp\u003eThe targeted \u003ctt\u003essh_sftpd\u003c/tt\u003e process enters an infinite tail-recursive loop. It never processes another message, its message queue grows without bound, and it can only be stopped by killing the process. BEAM\u0027s reduction-based scheduler preemption continues to function, so other processes on the node are not starved, but each stuck channel process consumes its full CPU time share continuously and accumulates unbounded message queue memory. Opening many channels amplifies the CPU and memory impact.\u003c/p\u003e\u003cp\u003eErlang/OTP SSH configurations using the default \u003ctt\u003emax_channels\u003c/tt\u003e setting (\u003ctt\u003einfinity\u003c/tt\u003e) allow an authenticated user to open unlimited channels per connection, amplifying the attack without requiring multiple TCP connections or authentications.\u003c/p\u003e\u003cp\u003eNo file contents, credentials, or write access are obtainable through this issue. The impact is limited to denial of service on targeted SFTP channels, with secondary CPU degradation and memory growth.\u003c/p\u003e\u003cp\u003eThis vulnerability is associated with program file \u003ctt\u003elib/ssh/src/ssh_sftpd.erl\u003c/tt\u003e and program routine \u003ctt\u003essh_sftpd:handle_data/4\u003c/tt\u003e.\u003c/p\u003e\u003cp\u003eThis issue affects OTP from OTP 17.0 before OTP\u0026nbsp;29.0.3, OTP\u0026nbsp;28.5.0.3 and OTP\u0026nbsp;27.3.4.14, corresponding to \u003ctt\u003essh\u003c/tt\u003e from 3.0.1 before 6.0.2, 5.5.2.2 and 5.2.11.9.\u003c/p\u003e\", \"base64\": false}]}], \"problemTypes\": [{\"descriptions\": [{\"lang\": \"en\", \"type\": \"CWE\", \"cweId\": \"CWE-835\", \"description\": \"CWE-835 Loop with Unreachable Exit Condition (\u0027Infinite Loop\u0027)\"}, {\"lang\": \"en\", \"type\": \"CWE\", \"cweId\": \"CWE-400\", \"description\": \"CWE-400 Uncontrolled Resource Consumption\"}]}], \"cpeApplicability\": [{\"nodes\": [{\"negate\": false, \"cpeMatch\": [{\"criteria\": \"cpe:2.3:a:erlang:erlang\\\\/otp:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"27.3.4.14\"}, {\"criteria\": \"cpe:2.3:a:erlang:erlang\\\\/otp:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"28.5.0.3\", \"versionStartIncluding\": \"28.0\"}, {\"criteria\": \"cpe:2.3:a:erlang:erlang\\\\/otp:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"29.0.3\", \"versionStartIncluding\": \"29.0\"}], \"operator\": \"OR\"}], \"operator\": \"AND\"}], \"providerMetadata\": {\"orgId\": \"6b3ad84c-e1a6-4bf7-a703-f496b71e49db\", \"shortName\": \"EEF\", \"dateUpdated\": \"2026-07-24T14:14:32.812Z\"}}}",
"cveMetadata": "{\"cveId\": \"CVE-2026-54886\", \"state\": \"PUBLISHED\", \"dateUpdated\": \"2026-07-24T14:14:32.812Z\", \"dateReserved\": \"2026-06-16T10:47:13.914Z\", \"assignerOrgId\": \"6b3ad84c-e1a6-4bf7-a703-f496b71e49db\", \"datePublished\": \"2026-07-02T16:06:20.502Z\", \"assignerShortName\": \"EEF\"}",
"dataType": "CVE_RECORD",
"dataVersion": "5.2"
}
}
}
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Sightings
| Author | Source | Type | Date |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or seen somewhere by the user.
- Confirmed: The vulnerability is confirmed from an analyst perspective.
- Published Proof of Concept: A public proof of concept is available for this vulnerability.
- Exploited: This vulnerability was exploited and seen by the user reporting the sighting.
- Patched: This vulnerability was successfully patched by the user reporting the sighting.
- Not exploited: This vulnerability was not exploited or seen by the user reporting the sighting.
- Not confirmed: The user expresses doubt about the veracity of the vulnerability.
- Not patched: This vulnerability was not successfully patched by the user reporting the sighting.
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