CVE-2026-23943 (GCVE-0-2026-23943)

Vulnerability from cvelistv5 – Published: 2026-03-13 09:11 – Updated: 2026-04-07 14:38
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 ?
6.9 (Medium)
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N
CWE
  • CWE-409 - Improper Handling of Highly Compressed Data (Data Amplification)
Assigner
EEF
References
Impacted products
Vendor Product Version
Erlang OTP Affected: 3.0.1 , < * (otp)
    cpe:2.3:a:erlang:erlang\/otp:*:*:*:*:*:*:*:*
 Create a notification for this product.
    Erlang OTP Affected: 17.0 , < * (otp)
Affected: 07b8f441ca711f9812fad9e9115bab3c3aa92f79 , < * (git)
    cpe:2.3:a:erlang:erlang\/otp:*:*:*:*:*:*:*:*
 Create a notification for this product.
Credits
Igor Morgenstern / Aisle Research Michał Wąsowski Jakub Witczak
Show details on NVD website
To clipboard 

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              "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"
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              "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"
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    "dateReserved": "2026-01-19T14:23:14.343Z",
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    "vulnrichment": {
      "containers": "{\"adp\": [{\"title\": \"CISA ADP Vulnrichment\", \"metrics\": [{\"other\": {\"type\": \"ssvc\", \"content\": {\"id\": \"CVE-2026-23943\", \"role\": \"CISA Coordinator\", \"options\": [{\"Exploitation\": \"none\"}, {\"Automatable\": \"yes\"}, {\"Technical Impact\": \"partial\"}], \"version\": \"2.0.3\", \"timestamp\": \"2026-03-13T16:01:40.898658Z\"}}}], \"providerMetadata\": {\"orgId\": \"134c704f-9b21-4f2e-91b3-4a467353bcc0\", \"shortName\": \"CISA-ADP\", \"dateUpdated\": \"2026-03-13T16:01:44.722Z\"}}], \"cna\": {\"title\": \"Pre-auth SSH DoS via unbounded zlib inflate\", \"source\": {\"discovery\": \"EXTERNAL\"}, \"credits\": [{\"lang\": \"en\", \"type\": \"reporter\", \"value\": \"Igor Morgenstern / Aisle Research\"}, {\"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\"}]}, {\"capecId\": \"CAPEC-490\", \"descriptions\": [{\"lang\": \"en\", \"value\": \"CAPEC-490 Amplification\"}]}], \"metrics\": [{\"format\": \"CVSS\", \"cvssV4_0\": {\"Safety\": \"NOT_DEFINED\", \"version\": \"4.0\", \"Recovery\": \"NOT_DEFINED\", \"baseScore\": 6.9, \"Automatable\": \"NOT_DEFINED\", \"attackVector\": \"NETWORK\", \"baseSeverity\": \"MEDIUM\", \"valueDensity\": \"NOT_DEFINED\", \"vectorString\": \"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N\", \"exploitMaturity\": \"NOT_DEFINED\", \"providerUrgency\": \"NOT_DEFINED\", \"userInteraction\": \"NONE\", \"attackComplexity\": \"LOW\", \"attackRequirements\": \"NONE\", \"privilegesRequired\": \"NONE\", \"subIntegrityImpact\": \"NONE\", \"vulnIntegrityImpact\": \"NONE\", \"subAvailabilityImpact\": \"NONE\", \"vulnAvailabilityImpact\": \"LOW\", \"subConfidentialityImpact\": \"NONE\", \"vulnConfidentialityImpact\": \"NONE\", \"vulnerabilityResponseEffort\": \"NOT_DEFINED\"}, \"scenarios\": [{\"lang\": \"en\", \"value\": \"GENERAL\"}]}], \"affected\": [{\"cpes\": [\"cpe:2.3:a:erlang:erlang\\\\/otp:*:*:*:*:*:*:*:*\"], \"repo\": \"https://github.com/erlang/otp\", \"vendor\": \"Erlang\", \"modules\": [\"ssh_transport\"], \"product\": \"OTP\", \"versions\": [{\"status\": \"affected\", \"changes\": [{\"at\": \"5.5.1\", \"status\": \"unaffected\"}, {\"at\": \"5.2.11.6\", \"status\": \"unaffected\"}, {\"at\": \"5.1.4.14\", \"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_transport.erl\"], \"defaultStatus\": \"unknown\", \"programRoutines\": [{\"name\": \"ssh_transport:decompress/2\"}, {\"name\": \"ssh_transport:handle_packet_part/4\"}]}, {\"cpes\": [\"cpe:2.3:a:erlang:erlang\\\\/otp:*:*:*:*:*:*:*:*\"], \"repo\": \"https://github.com/erlang/otp\", \"vendor\": \"Erlang\", \"modules\": [\"ssh_transport\"], \"product\": \"OTP\", \"versions\": [{\"status\": \"affected\", \"changes\": [{\"at\": \"28.4.1\", \"status\": \"unaffected\"}, {\"at\": \"27.3.4.9\", \"status\": \"unaffected\"}, {\"at\": \"26.2.5.18\", \"status\": \"unaffected\"}], \"version\": \"17.0\", \"lessThan\": \"*\", \"versionType\": \"otp\"}, {\"status\": \"affected\", \"changes\": [{\"at\": \"43a87b949bdff12d629a8c34146711d9da93b1b1\", \"status\": \"unaffected\"}, {\"at\": \"93073c3bd338c60cd2bae715ce6a1d4ffc1a8fd3\", \"status\": \"unaffected\"}, {\"at\": \"0c1c04b191f6ab940e8fcfabce39eb5a8a6440a4\", \"status\": \"unaffected\"}], \"version\": \"07b8f441ca711f9812fad9e9115bab3c3aa92f79\", \"lessThan\": \"*\", \"versionType\": \"git\"}], \"packageURL\": \"pkg:github/erlang/otp\", \"packageName\": \"erlang/otp\", \"programFiles\": [\"lib/ssh/src/ssh_transport.erl\"], \"collectionURL\": \"https://github.com\", \"defaultStatus\": \"unknown\", \"programRoutines\": [{\"name\": \"ssh_transport:decompress/2\"}, {\"name\": \"ssh_transport:handle_packet_part/4\"}]}], \"references\": [{\"url\": \"https://github.com/erlang/otp/security/advisories/GHSA-c836-qprm-jw9r\", \"tags\": [\"vendor-advisory\", \"related\"]}, {\"url\": \"https://cna.erlef.org/cves/CVE-2026-23943.html\", \"tags\": [\"related\"]}, {\"url\": \"https://osv.dev/vulnerability/EEF-CVE-2026-23943\", \"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/43a87b949bdff12d629a8c34146711d9da93b1b1\", \"tags\": [\"patch\"]}, {\"url\": \"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)\"}]}], \"configurations\": [{\"lang\": \"en\", \"value\": \"The SSH server or client must advertise zlib or zlib@openssh.com compression. Both are enabled by default. With zlib, the attack is pre-authentication; with zlib@openssh.com, authentication is required first.\", \"supportingMedia\": [{\"type\": \"text/html\", \"value\": \"The SSH server or client must advertise \u003ctt\u003ezlib\u003c/tt\u003e or \u003ctt\u003ezlib@openssh.com\u003c/tt\u003e compression. Both are enabled by default. With \u003ctt\u003ezlib\u003c/tt\u003e, the attack is pre-authentication; with \u003ctt\u003ezlib@openssh.com\u003c/tt\u003e, authentication is required first.\", \"base64\": false}]}], \"providerMetadata\": {\"orgId\": \"6b3ad84c-e1a6-4bf7-a703-f496b71e49db\", \"shortName\": \"EEF\", \"dateUpdated\": \"2026-04-07T14:38:05.652Z\"}}}",
      "cveMetadata": "{\"cveId\": \"CVE-2026-23943\", \"state\": \"PUBLISHED\", \"dateUpdated\": \"2026-04-07T14:38:05.652Z\", \"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

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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.



Detection rules are retrieved from Rulezet.