# CVE-2026-54886: SSH SFTP server denial of service via extended channel data infinite loop Status: published. Published: 2026-07-02. Updated: 2026-11-11. 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 27.3.4.14, OTP 28.5.0.3, and OTP 29.0.3, corresponding to ssh from 3.0.1 before 5.2.11.9, 5.5.2.2, and 6.0.2. Whether OTP before OTP 17.0, corresponding to ssh before 3.0.1, is affected is unknown. ## Remediation - workaround: * 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. * Set the max_sessions daemon option to limit total concurrent SSH connections to the daemon. * Use external process monitoring to detect and kill ssh_sftpd processes with abnormally high reduction counts and growing message queues. * Ensure that the SFTP server port is not reachable from untrusted machines. (source: CNA: EEF) - fix: The reporting source identifies this reference as a patch. Check the advisory for affected versions and supported release branches. (source: CNA: EEF) — https://github.com/erlang/otp/commit/eaf9550b8ad4738b81149d3f617102d980c6dd18 ## Affected products and versions - Erlang / OTP (otp): ≥ 17.0; < * (affected, otp); unaffected at 27.3.4.14; unaffected at 28.5.0.3; unaffected at 29.0.3. Source: CNA: EEF - Erlang / OTP (ssh): ≥ 3.0.1; < * (affected, otp); unaffected at 5.2.11.9; unaffected at 5.5.2.2; unaffected at 6.0.2. Source: CNA: EEF - Erlang / OTP (erlang/otp): ≥ 84adefa331c4159d432d22840663c38f155cd4c1; < eaf9550b8ad4738b81149d3f617102d980c6dd18 (affected, git); ≥ eaf9550b8ad4738b81149d3f617102d980c6dd18; < * (unaffected, git). Source: CNA: EEF ## Severity and prioritization - CVSS 4.0: 5.3 (medium); 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; source: CNA: EEF - CISA KEV: No listing in collected sources - EPSS: 0.33% as of 2026-11-10; percentile 26.49% - SSVC: exploitation none; automatable no; technical impact partial; source ADP: CISA-ADP - Weaknesses: CWE-835, CWE-400 ## Exploit evidence No exploit evidence in collected sources. This is not proof of no exploitation. ## References - https://github.com/erlang/otp/security/advisories/GHSA-7wp4-pc27-2vj9 (CNA: EEF; vendor-advisory, related) - https://cna.erlef.org/cves/CVE-2026-54886.html (CNA: EEF; related) - https://osv.dev/vulnerability/EEF-CVE-2026-54886 (CNA: EEF; related) - https://www.erlang.org/doc/system/versions.html#order-of-versions (CNA: EEF; x_version-scheme) - https://github.com/erlang/otp/commit/eaf9550b8ad4738b81149d3f617102d980c6dd18 (CNA: EEF; patch) ## Provenance - CNA: EEF: https://www.cve.org/CVERecord?id=CVE-2026-54886; retrieved 2026-11-11; source updated 2026-11-11 - FIRST EPSS: https://api.first.org/data/v1/epss?cve=CVE-2026-54886; retrieved 2026-11-11; source updated Not reported Revision: 39b148d91029664527e2d51bc725588367c0c58fa9a5054f21468892a04294cd Canonical: https://y2.dev/cve/CVE-2026-54886 ## Agent and API access Public CVE pages, Markdown, and JSON are free to read without an account or API key. - Public catalog: https://y2.dev/cve/index.json. 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