CVE-2026-23943 (GCVE-0-2026-23943)
Vulnerability from cvelistv5 – Published: 2026-03-13 09:11 – Updated: 2026-03-13 16:07
VLAI?
Title
Pre-auth SSH DoS via unbounded zlib inflate
Summary
Improper Handling of Highly Compressed Data (Compression Bomb) vulnerability in Erlang OTP ssh (ssh_transport modules) allows Denial of Service via Resource Depletion.
The SSH transport layer advertises legacy zlib compression by default and inflates attacker-controlled payloads pre-authentication without any size limit, enabling reliable memory exhaustion DoS.
Two compression algorithms are affected:
* zlib: Activates immediately after key exchange, enabling unauthenticated attacks
* zlib@openssh.com: Activates post-authentication, enabling authenticated attacks
Each SSH packet can decompress ~255 MB from 256 KB of wire data (1029:1 amplification ratio). Multiple packets can rapidly exhaust available memory, causing OOM kills in memory-constrained environments.
This vulnerability is associated with program files lib/ssh/src/ssh_transport.erl and program routines ssh_transport:decompress/2, ssh_transport:handle_packet_part/4.
This issue affects OTP from OTP 17.0 until OTP 28.4.1, 27.3.4.9 and 26.2.5.18 corresponding to ssh from 3.0.1 until 5.5.1, 5.2.11.6 and 5.1.4.14.
Severity ?
CWE
- CWE-409 - Improper Handling of Highly Compressed Data (Data Amplification)
Assigner
References
| URL | Tags | |
|---|---|---|
|
|
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Impacted products
Credits
Igor Morgenstern / Aisle Research
Michał Wąsowski
Jakub Witczak
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\"https://github.com/erlang/otp/commit/93073c3bd338c60cd2bae715ce6a1d4ffc1a8fd3\", \"tags\": [\"patch\"]}, {\"url\": \"https://github.com/erlang/otp/commit/0c1c04b191f6ab940e8fcfabce39eb5a8a6440a4\", \"tags\": [\"patch\"]}], \"workarounds\": [{\"lang\": \"en\", \"value\": \"Best workaround - Disable all compression:\\n\\n{preferred_algorithms, [{compression, [\u0027none\u0027]}]}\\n\\nAlternative mitigations (less secure):\\n\\n* Disable only pre-auth zlib compression (authenticated users can still exploit via zlib@openssh.com):\\n {modify_algorithms, [{rm, [{compression, [\u0027zlib\u0027]}]}]}\\n* Limit concurrent sessions (reduces attack surface but does not prevent exploitation):\\n {max_sessions, N} % Cap total concurrent sessions (default is infinity)\", \"supportingMedia\": [{\"type\": \"text/html\", \"value\": \"\u003cp\u003e\u003cb\u003eBest workaround - Disable all compression:\u003c/b\u003e\u003c/p\u003e\u003cpre\u003e{preferred_algorithms, [{compression, [\u0027none\u0027]}]}\u003c/pre\u003e\u003cp\u003e\u003cb\u003eAlternative mitigations (less secure):\u003c/b\u003e\u003c/p\u003e\u003cul\u003e\u003cli\u003eDisable only pre-auth zlib compression (authenticated users can still exploit via zlib@openssh.com):\u003cpre\u003e{modify_algorithms, [{rm, [{compression, [\u0027zlib\u0027]}]}]}\u003c/pre\u003e\u003c/li\u003e\u003cli\u003eLimit concurrent sessions (reduces attack surface but does not prevent exploitation):\u003cpre\u003e{max_sessions, N} % Cap total concurrent sessions (default is infinity)\u003c/pre\u003e\u003c/li\u003e\u003c/ul\u003e\", \"base64\": false}]}], \"x_generator\": {\"engine\": \"Vulnogram 0.2.0\"}, \"descriptions\": [{\"lang\": \"en\", \"value\": \"Improper Handling of Highly Compressed Data (Compression Bomb) vulnerability in Erlang OTP ssh (ssh_transport modules) allows Denial of Service via Resource Depletion.\\n\\nThe SSH transport layer advertises legacy zlib compression by default and inflates attacker-controlled payloads pre-authentication without any size limit, enabling reliable memory exhaustion DoS.\\n\\nTwo compression algorithms are affected:\\n\\n* zlib: Activates immediately after key exchange, enabling unauthenticated attacks\\n* zlib@openssh.com: Activates post-authentication, enabling authenticated attacks\\n\\nEach SSH packet can decompress ~255 MB from 256 KB of wire data (1029:1 amplification ratio). Multiple packets can rapidly exhaust available memory, causing OOM kills in memory-constrained environments.\\n\\nThis vulnerability is associated with program files lib/ssh/src/ssh_transport.erl and program routines ssh_transport:decompress/2, ssh_transport:handle_packet_part/4.\\n\\nThis issue affects OTP from OTP 17.0 until OTP 28.4.1, 27.3.4.9 and 26.2.5.18 corresponding to ssh from 3.0.1 until 5.5.1, 5.2.11.6 and 5.1.4.14.\", \"supportingMedia\": [{\"type\": \"text/html\", \"value\": \"Improper Handling of Highly Compressed Data (Compression Bomb) vulnerability in Erlang OTP ssh (ssh_transport modules) allows Denial of Service via Resource Depletion.\u003cp\u003eThe SSH transport layer advertises legacy zlib compression by default and inflates attacker-controlled payloads pre-authentication without any size limit, enabling reliable memory exhaustion DoS.\u003c/p\u003e\u003cp\u003eTwo compression algorithms are affected:\u003c/p\u003e\u003cul\u003e\u003cli\u003e\u003cb\u003ezlib:\u003c/b\u003e Activates immediately after key exchange, enabling unauthenticated attacks\u003c/li\u003e\u003cli\u003e\u003cb\u003ezlib@openssh.com:\u003c/b\u003e Activates post-authentication, enabling authenticated attacks\u003c/li\u003e\u003c/ul\u003e\u003cp\u003eEach SSH packet can decompress ~255 MB from 256 KB of wire data (1029:1 amplification ratio). Multiple packets can rapidly exhaust available memory, causing OOM kills in memory-constrained environments.\u003c/p\u003e\u003cp\u003eThis vulnerability is associated with program files \u003ctt\u003elib/ssh/src/ssh_transport.erl\u003c/tt\u003e and program routines \u003ctt\u003essh_transport:decompress/2\u003c/tt\u003e, \u003ctt\u003essh_transport:handle_packet_part/4\u003c/tt\u003e.\u003c/p\u003e\u003cp\u003eThis issue affects OTP from OTP 17.0 until OTP 28.4.1, 27.3.4.9 and 26.2.5.18 corresponding to ssh from 3.0.1 until 5.5.1, 5.2.11.6 and 5.1.4.14.\u003c/p\u003e\", \"base64\": false}]}], \"problemTypes\": [{\"descriptions\": [{\"lang\": \"en\", \"type\": \"CWE\", \"cweId\": \"CWE-409\", \"description\": \"CWE-409 Improper Handling of Highly Compressed Data (Data Amplification)\"}]}], \"providerMetadata\": {\"orgId\": \"6b3ad84c-e1a6-4bf7-a703-f496b71e49db\", \"shortName\": \"EEF\", \"dateUpdated\": \"2026-03-13T16:07:55.970Z\"}}}",
"cveMetadata": "{\"cveId\": \"CVE-2026-23943\", \"state\": \"PUBLISHED\", \"dateUpdated\": \"2026-03-13T16:07:55.970Z\", \"dateReserved\": \"2026-01-19T14:23:14.343Z\", \"assignerOrgId\": \"6b3ad84c-e1a6-4bf7-a703-f496b71e49db\", \"datePublished\": \"2026-03-13T09:11:57.794Z\", \"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 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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