Security readout for executives and security teams
Plain-English summary
Erlang/OTP’s SSH service can expand small compressed network packets into very large memory allocations. With legacy zlib compression, a remote attacker can trigger this before authentication, potentially exhausting memory, terminating the service, or causing system-level out-of-memory kills. The issue affects a broad range of OTP releases beginning with OTP 17.0.
Executive priority
Prioritize internet-facing or broadly reachable Erlang SSH services, especially on memory-limited infrastructure. Although rated medium with CVSS 4.0 score 6.9, pre-authentication resource exhaustion can interrupt availability. Patch exposed systems promptly; handle isolated or non-SSH deployments through normal risk-based maintenance after confirming exposure.
Technical view
The SSH transport decompresses attacker-controlled data without an output-size limit. A 256 KB packet may inflate to approximately 255 MB, a reported 1029:1 ratio. Legacy zlib is exploitable after key exchange but before authentication; zlib@openssh.com requires authentication. Affected logic includes ssh_transport:decompress/2 and ssh_transport:handle_packet_part/4.
Likely exposure
Exposure is highest where an affected Erlang/OTP SSH listener is reachable from untrusted networks and negotiates legacy zlib compression. Memory-constrained containers, appliances, and hosts may fail rapidly. Applications using Erlang/OTP without its SSH service, or running listed fixed versions, are not shown by the supplied evidence to be exposed.
Exploitation context
The attack requires network access and low complexity, with no privileges or user interaction for legacy zlib. Multiple compressed packets can cause reliable memory exhaustion. The supplied bundle reports no CISA KEV listing and provides no evidence of active exploitation in the wild as of its July 24, 2026 update.
Researcher notes
CWE-409 applies. The vulnerable files and routines are identified, and three upstream patch commits are supplied. The bundle’s affected-version metadata is less clear for obsolete branches; use the vendor advisory and Erlang version-ordering rules when evaluating exact releases. No confidentiality or integrity impact is reported.
Mitigation direction
- Upgrade OTP 28 to 28.4.1 or later.
- Upgrade OTP 27 to 27.3.4.9 or later.
- Upgrade OTP 26 to 26.2.5.18 or later.
- For other affected branches, follow the Erlang advisory and move to a supported fixed release.
- Until upgraded, restrict affected SSH listeners to trusted networks and monitor memory pressure.
Validation and detection
- Inventory Erlang/OTP and bundled ssh application versions across servers, containers, appliances, and embedded products.
- Identify whether the Erlang SSH service is enabled and reachable from untrusted networks.
- Confirm deployed versions meet the applicable fixed-release threshold stated in the vendor advisory.
- Review telemetry for memory spikes, out-of-memory kills, crashes, or repeated restarts involving Erlang SSH services.
- Validate remediation through version inspection and safe functional SSH testing without compressed attack traffic.
Public sources used
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
Conservative CVE-to-ATT&CK context
These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.
ATT&CK lookup starting points
Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.
CWE-409: Exact CWE lookup
Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.
Open ATT&CK lookupCVE-2026-23943 mapping review
Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.
Open ATT&CK lookup- Severity
- Medium
- CVSS
- 6.9 (4.0)
- Known Exploited
- No
- Published
Vector: 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
CNA and ADP enrichment extracted from CVE v5
These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.
SSVC decision data
CVSS vector scores
1 official scoreWe collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.
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——EEFVulnerability scoring details
Base CVSS 4.0 score
6.9MediumVector: 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
Vulnerability timeline
Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.
- CVE reservedCVE Program
The CVE ID was reserved by the assigning CNA.
- CVE publishedCVE Program
The CVE record was published.
- CVE updatedCVE Program
The CVE record metadata indicates this as the latest update time.
ADP provider summaries
Source materials
- CVE List V5 sourceCVE List V5
- https://github.com/erlang/otp/security/advisories/GHSA-c836-qprm-jw9rCVE reference, EEF · vendor-advisory, related
- https://cna.erlef.org/cves/CVE-2026-23943.htmlCVE reference, EEF · related
- https://osv.dev/vulnerability/EEF-CVE-2026-23943CVE reference, EEF · related
- https://www.erlang.org/doc/system/versions.html#order-of-versionsCVE reference, EEF · x_version-scheme
- https://github.com/erlang/otp/commit/43a87b949bdff12d629a8c34146711d9da93b1b1CVE reference, EEF · patch
- https://github.com/erlang/otp/commit/93073c3bd338c60cd2bae715ce6a1d4ffc1a8fd3CVE reference, EEF · patch
- https://github.com/erlang/otp/commit/0c1c04b191f6ab940e8fcfabce39eb5a8a6440a4CVE reference, EEF · patch
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.
Improper Handling of Highly Compressed Data (Data Amplification)
Improper Handling of Highly Compressed Data (Data Amplification) represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.