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.

Published May 7, 2026Updated Sep 18, 2026Sources: cvelistV5, Go

Triage

Is it exploited, how likely is exploitation, what does it touch, and how severe do the scoring sources call it.

Exploitation

Unreported

no source claims exploitation

EPSS

chance of exploitation in 30 days

Affects

go standard library

109 products listed

CVSS base

7.5

HIGH

CISA SSVC assessment

Three decision points CISA publishes for the CVEs it assesses · SSVC 2.0.3. A stakeholder decision, not a severity score.

CISA

Exploitation

None

none · proof-of-concept · active

Automatable

Yes

can an attacker script all four kill-chain steps

Technical impact

Partial

partial · total control of the vulnerable component

Affected scope

The catalog records vendors and products as separate lists, not pairs, so which product belongs to which vendor is not something this page can say.

Vendors (2)

go standard library redhat

Products (109)

net mailred hat ansible automation platform 2 5 for rhel 8red hat ansible automation platform 2 5 for rhel 9red hat ansible automation platform 2 6 for rhel 9red hat enterprise linux 10red hat enterprise linux 10 0 extended update supportred hat enterprise linux 8red hat enterprise linux 8 8 telecommunications update servicered hat enterprise linux 8 8 update services for sap solutionsred hat enterprise linux 9red hat enterprise linux 9 2 update services for sap solutionsred hat enterprise linux 9 4 update services for sap solutionsred hat enterprise linux 9 6 extended update supportred hat openshift container platform 4 12red hat openshift container platform 4 13red hat openshift container platform 4 16red hat openshift container platform 4 17red hat openshift container platform 4 18red hat openshift container platform 4 19rhem 1 1 for rhel 10rhem 1 1 for rhel 9cert manager support for red hat openshift release 1 19logging for red hat openshift 6logging for red hat openshift 6 2logging subsystem for red hat openshift 6 4logging subsystem for red hat openshift 6 5multicluster engine for kubernetes 2 11openshift api for data protection 1 3openshift api for data protection 1 4openshift api for data protection 1 5openshift api for data protection 1 6red hat advanced cluster security 4 9red hat advanced cluster security for kubernetes 4 10red hat developer hub 1 10red hat developer hub 1 9red hat hardened imagesred hat migration toolkit 1 8red hat migration toolkit for applications 8 1red hat migration toolkit for applications 8 2red hat openshift ai 2 25red hat openshift ai 3 4red hat openshift container platform 4 14red hat openshift container platform 4 20red hat openshift container platform 4 21red hat openshift dev spaces 3 30red hat openshift distributed tracing 3 10 2red hat openshift service mesh 3 0red hat openshift service mesh 3 1red hat openshift service mesh 3 2red hat openshift service mesh 3 3red hat openshift workload availability 0 12red hat openshift workload availability 0 13red hat openshift workload availability 0 3red hat openshift workload availability 0 7red hat openshift workload availability 0 8red hat openshift workload availability 5 7red hat quay 3 10red hat quay 3 12red hat quay 3 15red hat quay 3 16red hat quay 3 9red hat trusted artifact signer 1 4assisted installer for red hat openshift container platform 2confidential compute attestationcryostat 4custom metric autoscaler operator for red hat openshiftexternaldns operatorexternal secrets operator for red hat openshiftfile integrity operatorgatekeeper 3logical volume manager storagemultiarch tuning operatormulticluster engine for kubernetesmulticluster global hubnetwork observability operatoropenshift developer tools and servicesopenshift lightspeedopenshift pipelinesopenshift serverlessopenshift service mesh 2openshift service mesh 3power monitoring for red hat openshiftred hat advanced cluster management for kubernetes 2red hat ansible automation platform 2red hat ceph storage 5red hat ceph storage 6red hat ceph storage 9red hat certification program for red hat enterprise linux 9red hat edge manager 1red hat enterprise linux ai rhel ai 3red hat lightspeed for runtimes operatorred hat openshift ai rhoaired hat openshift cluster manager clired hat openshift container platform 4red hat openshift data foundation 4red hat openshift dev workspaces operatorred hat openshift for windows containersred hat openshift gitopsred hat openshift virtualization 4red hat openstack platform 16 2red hat openstack platform 17 1red hat openstack platform 18 0red hat quay 3red hat satellite 6red hat service interconnect 1red hat service interconnect 2security profiles operatorzero trust workload identity managerzero trust workload identity manager tech preview

Every base score collected

Sources score independently and disagree; each row says who scored it and under which version.

Score	Version	Severity	Expl.	Impact	Source
7.5	CVSS 3.1	HIGH	—	—	cvelistV5

Weakness & attack patterns

CWE-606

References

25 on the record

go.dev/issue/78566
reference
go.dev/cl/759940
reference
groups.google.com/g/golang-announce/c/qcCIEXso47M
reference
pkg.go.dev/vuln/GO-2026-4986
reference
access.redhat.com/security/cve/CVE-2026-39820
vdb-entry, x_refsource_REDHAT
bugzilla.redhat.com/show_bug.cgi?id=2467820
issue-tracking, x_refsource_REDHAT
security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-39820.json
x_sadp-csaf-vex
access.redhat.com/errata/RHSA-2026:68334
vendor-advisory, x_refsource_REDHAT

Elsewhere on this site

go standard libraryevery CVE for this vendor
redhatevery CVE for this vendor
CWE-606other pages naming this weakness

Not in any source we poll

Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.

No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
No exploit packet captures, log samples, or incident case IDs supplied.