CVE-2026-54886 (GCVE-0-2026-54886)
Vulnerability from cvelistv5 – Published: 2026-07-02 16:06 – Updated: 2026-07-03 04:29
VLAI
Title
SSH SFTP server denial of service via extended channel data infinite loop
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 until OTP 29.0.3, 28.5.0.3, and 27.3.4.14 corresponding to ssh from 3.0.1 until 6.0.2, 5.5.2.2, and 5.2.11.9.
Severity
SSVC
Exploitation: none
Automatable: no
Technical Impact: partial
CISA Coordinator (v2.0.3)
CWE
Assigner
References
5 references
| URL | Tags |
|---|---|
| https://github.com/erlang/otp/security/advisories… | vendor-advisoryrelated |
| https://cna.erlef.org/cves/CVE-2026-54886.html | related |
| https://osv.dev/vulnerability/EEF-CVE-2026-54886 | related |
| https://www.erlang.org/doc/system/versions.html#o… | x_version-scheme |
| https://github.com/erlang/otp/commit/eaf9550b8ad4… | patch |
Impacted products
2 products
Credits
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"containers": "{\"adp\": [{\"title\": \"CISA ADP Vulnrichment\", \"metrics\": [{\"other\": {\"type\": \"ssvc\", \"content\": {\"id\": \"CVE-2026-54886\", \"role\": \"CISA Coordinator\", \"options\": [{\"Exploitation\": \"none\"}, {\"Automatable\": \"no\"}, {\"Technical Impact\": \"partial\"}], \"version\": \"2.0.3\", \"timestamp\": \"2026-07-02T17:27:25.414155Z\"}}}], \"providerMetadata\": {\"orgId\": \"134c704f-9b21-4f2e-91b3-4a467353bcc0\", \"shortName\": \"CISA-ADP\", \"dateUpdated\": \"2026-07-02T17:27:27.846Z\"}}], \"cna\": {\"title\": \"SSH SFTP server denial of service via extended channel data infinite loop\", \"source\": {\"discovery\": \"EXTERNAL\"}, \"credits\": [{\"lang\": \"en\", \"type\": \"finder\", \"value\": \"Lukas Backstr\\u00f6m\"}, {\"lang\": \"en\", \"type\": \"remediation developer\", \"value\": \"Micha\\u0142 W\\u0105sowski\"}, {\"lang\": \"en\", \"type\": \"remediation reviewer\", \"value\": \"Jakub Witczak\"}], \"impacts\": [{\"capecId\": \"CAPEC-130\", \"descriptions\": [{\"lang\": \"en\", \"value\": \"CAPEC-130 Excessive Allocation\"}]}], \"metrics\": [{\"format\": \"CVSS\", \"cvssV4_0\": {\"version\": \"4.0\", \"baseScore\": 5.3, \"attackVector\": \"NETWORK\", \"baseSeverity\": \"MEDIUM\", \"vectorString\": \"CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N\"}, \"scenarios\": [{\"lang\": \"en\", \"value\": \"GENERAL\"}]}], \"affected\": [{\"cpes\": [\"cpe:2.3:a:erlang:erlang\\\\/otp:*:*:*:*:*:*:*:*\"], \"repo\": \"https://github.com/erlang/otp\", \"vendor\": \"Erlang\", \"modules\": [\"ssh_sftpd\"], \"product\": \"OTP\", \"versions\": [{\"status\": \"affected\", \"changes\": [{\"at\": \"6.0.2\", \"status\": \"unaffected\"}, {\"at\": \"5.5.2.2\", \"status\": \"unaffected\"}, {\"at\": \"5.2.11.9\", \"status\": \"unaffected\"}], \"version\": \"3.0.1\", \"lessThan\": \"*\", \"versionType\": \"otp\"}], \"packageURL\": \"pkg:otp/ssh?repository_url=https:%2F%2Fgithub.com%2Ferlang%2Fotp\u0026vcs_url=git%20https:%2F%2Fgithub.com%2Ferlang%2Fotp.git\", \"packageName\": \"ssh\", \"programFiles\": [\"src/ssh_sftpd.erl\"], \"defaultStatus\": \"unaffected\", \"programRoutines\": [{\"name\": \"ssh_sftpd:handle_data/4\"}]}, {\"cpes\": [\"cpe:2.3:a:erlang:erlang\\\\/otp:*:*:*:*:*:*:*:*\"], \"repo\": \"https://github.com/erlang/otp\", \"vendor\": \"Erlang\", \"modules\": [\"ssh_sftpd\"], \"product\": \"OTP\", \"versions\": [{\"status\": \"affected\", \"changes\": [{\"at\": \"29.0.3\", \"status\": \"unaffected\"}, {\"at\": \"28.5.0.3\", \"status\": \"unaffected\"}, {\"at\": \"27.3.4.14\", \"status\": \"unaffected\"}], \"version\": \"17.0\", \"lessThan\": \"*\", \"versionType\": \"otp\"}, {\"status\": \"affected\", \"version\": \"84adefa3318eef8631bf25cd233246a86eea18cd\", \"lessThan\": \"eaf9550b8ad4738b81149d3f617102d980c6dd18\", \"versionType\": \"git\"}], \"packageURL\": \"pkg:github/erlang/otp\", \"packageName\": \"erlang/otp\", \"programFiles\": [\"lib/ssh/src/ssh_sftpd.erl\"], \"collectionURL\": \"https://github.com\", \"defaultStatus\": \"unaffected\", \"programRoutines\": [{\"name\": \"ssh_sftpd:handle_data/4\"}]}], \"references\": [{\"url\": \"https://github.com/erlang/otp/security/advisories/GHSA-7wp4-pc27-2vj9\", \"tags\": [\"vendor-advisory\", \"related\"]}, {\"url\": \"https://cna.erlef.org/cves/CVE-2026-54886.html\", \"tags\": [\"related\"]}, {\"url\": \"https://osv.dev/vulnerability/EEF-CVE-2026-54886\", \"tags\": [\"related\"]}, {\"url\": \"https://www.erlang.org/doc/system/versions.html#order-of-versions\", \"tags\": [\"x_version-scheme\"]}, {\"url\": \"https://github.com/erlang/otp/commit/eaf9550b8ad4738b81149d3f617102d980c6dd18\", \"tags\": [\"patch\"]}], \"workarounds\": [{\"lang\": \"en\", \"value\": \"* Set the max_channels daemon option to a finite value (e.g., {max_channels, 10}) to limit the number of channels an attacker can open per connection.\\n* Set the max_sessions daemon option to limit total concurrent SSH connections to the daemon.\\n* Use external process monitoring to detect and kill ssh_sftpd processes with abnormally high reduction counts and growing message queues.\\n* Ensure that the SFTP server port is not reachable from untrusted machines.\", \"supportingMedia\": [{\"type\": \"text/html\", \"value\": \"\u003cul\u003e\u003cli\u003eSet the \u003ctt\u003emax_channels\u003c/tt\u003e daemon option to a finite value (e.g., \u003ctt\u003e{max_channels, 10}\u003c/tt\u003e) to limit the number of channels an attacker can open per connection.\u003c/li\u003e\u003cli\u003eSet the \u003ctt\u003emax_sessions\u003c/tt\u003e daemon option to limit total concurrent SSH connections to the daemon.\u003c/li\u003e\u003cli\u003eUse external process monitoring to detect and kill \u003ctt\u003essh_sftpd\u003c/tt\u003e processes with abnormally high reduction counts and growing message queues.\u003c/li\u003e\u003cli\u003eEnsure that the SFTP server port is not reachable from untrusted machines.\u003c/li\u003e\u003c/ul\u003e\", \"base64\": false}]}], \"x_generator\": {\"engine\": \"cvelib 1.8.0\"}, \"descriptions\": [{\"lang\": \"en\", \"value\": \"Loop with Unreachable Exit Condition (\u0027Infinite Loop\u0027) vulnerability in Erlang OTP ssh (ssh_sftpd module) allows an authenticated SFTP user to render an SFTP channel permanently unresponsive.\\n\\nThe 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.\\n\\nThe 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.\\n\\nThe 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\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.\\n\\nErlang/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.\\n\\nNo 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.\\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 until OTP 29.0.3, 28.5.0.3, and 27.3.4.14 corresponding to ssh from 3.0.1 until 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 until OTP 29.0.3, 28.5.0.3, and 27.3.4.14 corresponding to \u003ctt\u003essh\u003c/tt\u003e from 3.0.1 until 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\": \"2026-07-03T04:29:26.056Z\"}}}",
"cveMetadata": "{\"cveId\": \"CVE-2026-54886\", \"state\": \"PUBLISHED\", \"dateUpdated\": \"2026-07-03T04:29:26.056Z\", \"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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Experimental. This forecast is provided for visualization only and may change without notice. Do not use it for operational decisions.
Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.
Sightings
| Author | Source | Type | Date | Other |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or observed by the user.
- Confirmed: The vulnerability has been validated from an analyst's perspective.
- Published Proof of Concept: A public proof of concept is available for this vulnerability.
- Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
- Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
- Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
- Not confirmed: The user expressed doubt about the validity of the vulnerability.
- Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.
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