CVE-2026-54886: Loop with Unreachable Exit Condition ('Infinite Loop') vulnerability in Erlang OTP ssh (ssh_sftpd module) allows an authenticated SFTP user to render ...

Description

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.

Metrics

CVSS 3.1

4.3/10

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L

CVSS 4.0

5.3/10

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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

EPSS Probability

0.33%

25.5th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

Affected Software

Vendor	Product	Versions
Erlang	Erlang\/Otp	>= 17.0, < 27.3.4.14
Erlang	Erlang\/Otp	>= 28.0, < 28.5.0.3
Erlang	Erlang\/Otp	>= 29.0, < 29.0.3
Erlang	Erlang\/Ssh	>= 3.0.1, < 5.2.11.9
Erlang	Erlang\/Ssh	>= 5.3, < 5.5.2.2
Erlang	Erlang\/Ssh	>= 6.0, < 6.0.2

References

https://cna.erlef.org/cves/CVE-2026-54886.htmlMitigation, Vendor Advisory
https://github.com/erlang/otp/commit/eaf9550b8ad4738b81149d3f617102d980c6dd18Patch
https://github.com/erlang/otp/security/advisories/GHSA-7wp4-pc27-2vj9Mitigation, Vendor Advisory
https://osv.dev/vulnerability/EEF-CVE-2026-54886Mitigation, Third Party Advisory
https://www.erlang.org/doc/system/versions.html#order-of-versionsRelease Notes

Timeline

Published: Jul 2, 2026
Last Modified: Jul 24, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2026-54886?

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.

How severe is CVE-2026-54886?

CVE-2026-54886 has a CVSS score of 4.3/10 (MEDIUM severity). The EPSS model estimates a 0.33% probability of exploitation in the next 30 days.

How do I fix CVE-2026-54886?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

How Strix Helps

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