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CVE Record

CVE-2026-39829: Invoking pathological RSA/DSA parameters may cause DoS in golang.org/x/crypto/ssh

The RSA and DSA public key parsers did not enforce size limits on key parameters. A crafted public key with an excessively large modulus or DSA parameter could cause several minutes of CPU consumption during signature verification. This could be triggered by unauthenticated clients during public key authentication. RSA moduli are now limited to 8192 bits, and DSA parameters are validated per FIPS 186-2.

HighCVSS 7.5Not KEV-listedUpdated
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Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

A flaw in the Go SSH library lets an unauthenticated attacker send an oversized RSA or DSA public key that ties up server CPU for minutes during login. Repeated attempts can starve the service and disrupt SSH-dependent workflows. It is a denial-of-service issue, not data theft, but any Go-based SSH server or tool is potentially exposed until upstream fixes are applied.

Executive priority

Treat as a standard high-severity availability patch cycle. It will not leak data, but a single unauthenticated attacker can degrade SSH-dependent operations such as deployments, admin access, and Git workflows. Schedule patching in the next planned maintenance window and accelerate for any internet-facing Go SSH endpoints.

Technical view

The RSA and DSA public key parsers in golang.org/x/crypto/ssh did not cap key parameter sizes. A crafted key with a huge modulus or DSA parameters caused expensive signature verification during public key authentication, triggered pre-authentication. The upstream fix caps RSA moduli at 8192 bits and validates DSA parameters per FIPS 186-2. CVSS 3.1 base is 7.5 (AV:N/AC:L/PR:N/UI:N/A:H). CWE-1176 and CWE-1284 are cited.

Likely exposure

Any service embedding golang.org/x/crypto/ssh as a server that accepts public key authentication from untrusted networks is exposed. That includes Go-based bastions, Git hosting daemons, CI runners, and container tooling. Red Hat has shipped multiple RHSA advisories, indicating meaningful downstream reach across Kubernetes and OpenShift components. KEV does not list this CVE.

Exploitation context

No active exploitation is cited in the sources and the CVE is not in CISA KEV. The precondition is network reach to an SSH endpoint that will attempt key verification; no credentials or user interaction are required. Impact is availability only. Public references describe the flaw at a design level, not weaponized proof-of-concept code.

Researcher notes

Root cause is missing input validation on asymmetric key parameters before verification, matching CWE-1284. Fix caps RSA moduli at 8192 bits and enforces FIPS 186-2 DSA parameter checks. Pre-auth reachability makes this attractive for opportunistic DoS against bastions. Watch for downstream consumers such as Kubernetes, Terraform providers, and CI agents that vendor x/crypto and lag upstream updates.

Mitigation direction

  • Upgrade golang.org/x/crypto to the fixed release referenced by GO-2026-5018 and rebuild affected services.
  • Apply the relevant Red Hat RHSA errata to OpenShift, RHEL, and container images that ship affected Go binaries.
  • Where patching is delayed, restrict SSH exposure to trusted networks or place a rate-limiting proxy in front.
  • Inventory internal Go-based SSH servers and tools that vendor x/crypto/ssh and prioritize by internet exposure.
  • Confirm connection and authentication timeouts are enforced so slow verifications drop rather than accumulate.

Validation and detection

  • Run govulncheck against built binaries to confirm GO-2026-5018 no longer resolves against your modules.
  • Inspect go.mod and go.sum for golang.org/x/crypto versions below the fixed release across all services.
  • Cross-check installed RPMs against RHSA-2026:36796, 36199, 37072, and related errata for affected hosts.
  • Monitor SSH server CPU and authentication latency for spikes correlated with unauthenticated key attempts.
  • After patching, verify SSH daemons reject oversized RSA moduli and non-conforming DSA parameters in test.
Prepared
Confidence
high
Sources
12

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-1176: 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-1284: 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-2026-39829 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
High
CVSS
7.5 (3.1)
Known Exploited
No
Published

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/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
33Source 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
7.5CVSS 3.1HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H3.93.6CISA-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

7.5High
CVSS 3.1 vector shape for CVE-2026-39829Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/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 crafted public key with excessive parameters
other:Red Hat severity ratingcvssV3_1
  • 2026-05-22T04:01:30.092Z: Reported to Red Hat.
  • 2026-05-22T02:31:27.324Z: 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-1176CWE-1284

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