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CVE Record

CVE-2026-39830: Invoking client can cause server deadlock on unexpected responses in golang.org/x/crypto/ssh

A malicious SSH peer could send unsolicited global request responses to fill an internal buffer, blocking the connection's read loop. The blocked goroutine could not be released by calling Close(), resulting in a resource leak per connection. Unsolicited global responses are now discarded.

CriticalCVSS 9.1Not KEV-listedUpdated
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Glexia's TakeAutomated analysiscritical

Security readout for executives and security teams

Plain-English summary

A malicious SSH server can cause a Go application using the affected SSH client library to stop processing a connection and retain resources. Repeated connections could degrade or exhaust service capacity. The supplied record rates this critical, but the affected-version data is incomplete, so organizations must confirm exposure against the Go advisory.

Executive priority

Treat confirmed exposure as an urgent availability risk, especially for services making many outbound SSH connections or reaching untrusted peers. Prioritize dependency inventory immediately, then patch and redeploy confirmed affected applications. Do not claim compromise solely from resource growth; investigate telemetry and connection destinations.

Technical view

Unsolicited SSH global-request responses can fill an internal buffer and block the connection read loop. Calling Close() does not release the blocked goroutine, producing a per-connection resource leak and potential deadlock. The corrected behavior discards unsolicited global responses. The record maps this to CWE-772 and CWE-833.

Likely exposure

Potentially exposed systems are Go applications using golang.org/x/crypto/ssh as an SSH client and connecting to malicious or untrusted SSH peers. Internet reachability increases opportunity but is not required. The supplied version entry is ambiguous and defaults to unaffected, so it cannot establish which deployed versions are vulnerable.

Exploitation context

The condition is remotely triggerable by a malicious SSH peer without privileges or user interaction, according to the supplied CVSS vector. No CISA KEV listing or other supplied evidence establishes active exploitation. The bundle also provides no evidence of public weaponization or observed attacks.

Researcher notes

The documented impact is a blocked read loop and unreleasable goroutine per malicious connection. Although the supplied CVSS includes high confidentiality impact, the narrative evidence describes resource exhaustion and availability loss, not a data-disclosure mechanism. Exact vulnerable and fixed versions are absent from the bundle; consult the linked Go advisory before drawing version conclusions.

Mitigation direction

  • Check GO-2026-5017 and the Go announcement for affected and corrected versions.
  • Update golang.org/x/crypto/ssh to the vendor-designated corrected release.
  • Rebuild and redeploy applications that statically include the affected dependency.
  • Apply relevant Red Hat errata where the dependency comes from supported Red Hat packages.
  • Restrict SSH client connections to trusted destinations until remediation is verified.

Validation and detection

  • Inventory applications and binaries containing golang.org/x/crypto/ssh.
  • Compare resolved dependency versions with the Go vulnerability advisory.
  • Confirm rebuilt artifacts contain the corrected library version.
  • Exercise SSH connection cleanup defensively in staging and check for retained goroutines.
  • Monitor connection counts, goroutines, memory, and service availability for unexplained growth.
Prepared
Confidence
medium
Sources
7

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

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 · low confidence lookup

CWE-772: 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 lookup
cwe · low confidence lookup

CWE-833: 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 lookup
cve · low confidence lookup

CVE-2026-39830 mapping review

Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.

Open ATT&CK lookup
Vulnerability profileCVE Program record
Severity
Critical
CVSS
9.1 (3.1)
Known Exploited
No
Published

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

Official CVE source material

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.

2CVSS vectors
5Timeline events
2ADP providers
43Source links

SSVC decision data

CISA-ADPCISA Coordinator
Timestamp
Version
2.0.3
Exploitation: noneAutomatable: yesTechnical Impact: partial

CVSS vector scores

2 official scores

We 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.

ScoreVersionSeverityVectorExploitImpactSource
9.1CVSS 3.1CriticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H3.95.2CISA-ADP
7.5CVSS 3.1HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H3.93.6redhat-SADP

Vulnerability scoring details

Base CVSS 3.1 score

9.1Critical
CVSS 3.1 vector shape for CVE-2026-39830Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

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

Attack Vector
NetworkAdjacentLocalPhysical
Attack Complexity
LowHigh
Privileges Required
NoneLowHigh
User Interaction
NoneRequired
Scope
ChangedUnchanged
Confidentiality Impact
HighLowNone
Integrity Impact
HighLowNone
Availability Impact
HighLowNone

Vulnerability timeline

Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.

  1. CVE reservedCVE Program

    The CVE ID was reserved by the assigning CNA.

  2. ADP timelineredhat-SADP

    Made public.

  3. CVE publishedCVE Program

    The CVE record was published.

  4. ADP timelineredhat-SADP

    Reported to Red Hat.

  5. CVE updatedCVE Program

    The CVE record metadata indicates this as the latest update time.

ADP provider summaries

CISA-ADPCISA ADP Vulnrichment
cvssV3_1other:ssvc
redhat-SADPgolang.org/x/crypto/ssh: golang.org/x/crypto/ssh: Denial of Service via resource leak from unsolicited SSH responses
other:Red Hat severity ratingcvssV3_1
  • 2026-05-22T04:01:38.517Z: Reported to Red Hat.
  • 2026-05-22T02:31:27.208Z: Made public.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
golang.org/x/cryptogolang.org/x/crypto/sshgolang.org/x/crypto/ssh, 0unaffected
Weakness

CWE details

CWE-772CWE-833

CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.

CWE-772 · source CWE mapping

Missing Release of Resource after Effective Lifetime

Missing Release of Resource after Effective Lifetime represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.

Open CWE intelligenceSame-CWE CVEs
CWE-833 · source CWE mapping

Deadlock

Deadlock represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.

Open CWE intelligenceSame-CWE CVEs