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CVE Record

CVE-2026-39820: Quadratic string concatentation in consumeComment in net/mail

Well-crafted inputs reaching ParseAddress, ParseAddressList, and ParseDate were able to trigger excessive CPU exhaustion and memory allocations.

HighCVSS 7.5Not KEV-listedUpdated
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Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

This vulnerability lets specially crafted email-like input make Go’s net/mail parsing functions consume excessive CPU and memory. The business impact is availability: services that parse attacker-controlled addresses or dates could slow down or fail. The source bundle does not show data theft, integrity impact, or confirmed exploitation.

Executive priority

Prioritize patching internet-facing or mail-processing Go services because the likely impact is service disruption. Treat it as high availability risk, not a confidentiality breach, based on the provided evidence.

Technical view

CVE-2026-39820 affects Go standard library net/mail parsing paths: ParseAddress, ParseAddressList, and ParseDate. Well-crafted inputs can trigger quadratic string concatenation in consumeComment, causing CPU exhaustion and memory allocations. CVSS 3.1 is 7.5 with network, low-complexity, unauthenticated availability impact.

Likely exposure

Exposure is most likely in Go applications or bundled products that parse untrusted mail addresses, address lists, or date headers using net/mail. Red Hat advisories are listed, but exact downstream package status must be verified per advisory.

Exploitation context

The bundle marks KEV as false and provides no cited evidence of active exploitation. The CVSS vector indicates remote, unauthenticated denial-of-service potential without user interaction, but the sources provided do not include public exploit status.

Researcher notes

Key uncertainty is exact fixed version and downstream product impact; the bundle names advisories but not their detailed status. Validation should focus on reachable parser use with attacker-controlled input and vendor-confirmed version mapping.

Mitigation direction

  • Check Go advisory GO-2026-4986 for affected and fixed versions.
  • Apply applicable Go or vendor updates from official advisories.
  • Review Red Hat errata for impacted downstream products.
  • Limit size and processing time for untrusted mail header input.
  • Avoid routing untrusted input to net/mail parsers until patched.

Validation and detection

  • Inventory services built with Go that parse email addresses or dates.
  • Search code for net/mail ParseAddress, ParseAddressList, and ParseDate usage.
  • Confirm Go toolchain and runtime versions against vendor advisories.
  • Verify Red Hat package status using listed RHSA and CSAF entries.
  • Monitor CPU and memory anomalies around mail parsing endpoints.
Prepared
Confidence
medium
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-407: 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.

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cwe · low confidence lookup

CWE-606: 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-2026-39820 mapping review

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

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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
18Source 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-2026-39820Attack 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-SADPnet/mail: golang: Go net/mail: Denial of Service via crafted email inputs
other:Red Hat severity ratingcvssV3_1
  • 2026-05-07T20:01:27.800Z: Reported to Red Hat.
  • 2026-05-07T19:41:19.854Z: Made public.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
Go standard librarynet/mailnet/mail, 0, 1.26.0-0unaffected
Weakness

CWE details

CWE-407CWE-606

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

CWE-407 · source CWE mapping

Inefficient Algorithmic Complexity

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

Open CWE intelligenceSame-CWE CVEs
CWE-606 · source CWE mapping

Unchecked Input for Loop Condition

Unchecked Input for Loop Condition represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.

Open CWE intelligenceSame-CWE CVEs