Medium File handling

CVE-2026-39819 — Invoking "go bug" follows symlinks in predictable temporary filenames in cmd/go

The "go bug" command writes to two files with predictable names in the system temporary directory (for example, "/tmp"). An attacker with access to the temporary directory can create a symlink in one of these names, causing "go bug" to overwrite the target of the symlink.

Published May 7, 2026 · Updated Oct 13, 2026 · Sources: NIST National Vulnerability Database, CVE Program (cve.org) e CISA ADP · CNA: Go

Low

Who exploits it and how urgent it is

A 0–100 score combining confirmed exploitation, ransomware and APT use, public exploits, EPSS and severity.

No exploitation signal in the sources consulted so far.

How the score was calculated

EPSS 0.1% (30-day exploitation probability)+1
Technical severity (medium)+3

The score orders the patch queue; it does not replace your asset context (internet exposure, criticality, compensating controls).

Triage

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

Exploitation

Not confirmed

Not in CISA KEV — an absence of record, not proof it is unexploited.

EPSS FIRST

0.15%

ahead of 4% of scored CVEs · Oct 14, 2026

Affects

Go toolchain

Cmd/go and 1 more

CVSS base

5.3

Medium · 3 source(s)

CISA SSVC assessment CISA

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

Exploitation

None

none · proof-of-concept · active

Automatable

can an attacker script the kill-chain steps

Technical impact

Partial

partial · total control of the vulnerable component

Remediation

Fixes and mitigations documented by the sources — linked to the original advisory.

Documented patch — go.dev (NIST National Vulnerability Database)

First 24 hours

Ordered from the record’s own fields — exposure first, because you cannot patch what you have not found. A rule-generated starting point.

Identify exposed assets running the affected vendor/product/version combinations (Go toolchain Cmd/go, Golang Go).
Apply the fixed version or the patch documented under Remediation.
Search available logs for exploit probes matching the vulnerability class (file handling), errors and authentication anomalies.

Affected scope

Vendor, product and versions as the sources word them.

Vendor	Product	Versions	Status	Source
Go toolchain	Cmd/go	< 1.25.10≥ 1.26.0-0 and < 1.26.3	Vulnerable	CVE Program (cve.org) e CISA ADP
Golang	Go	< 1.25.10≥ 1.26.0 and < 1.26.3	Vulnerable	NIST National Vulnerability Database

Attack characteristics

The CVSS vector, decoded. It describes the attack, not your exposure to it.

Attack vector

Local

Attack complexity

High

Privileges required

Low

User interaction

None

Scope

Unchanged

Confidentiality

Low

Integrity

High

Availability

None

Every base score collected

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

Score	Version	Severity	Expl.	Impact	Scored by
5.3	CVSS 3.1	Medium	1.0	4.2	nvd@nist.gov via NIST National Vulnerability Database
5.3	CVSS 3.1	Medium	1.0	4.2	134c704f-9b21-4f2e-91b3-4a467353bcc0 via NIST National Vulnerability Database
5.3	CVSS 3.1	Medium	—	—	CISA-ADP via CVE Program (cve.org) e CISA ADP

CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:H/A:N (score shown at the top: nvd@nist.gov)

Weakness MITRE

Weakness class according to MITRE’s CWE catalog.

CWE-59 · Link Following

Other CVEs with this weakness →

EPSS over time FIRST

Oct 13, 2026 → Oct 14, 2026 · 2 reading(s) · max 0.15%

Detection

Read off the CVSS vector and the weakness class. Starting points, not tested rules.

Local/physical vector: focus on endpoint telemetry (EDR) from affected hosts.
Monitor file creation in web directories and paths with traversal sequences (../).

endpoint telemetry (EDR)file integrity (FIM)

Timeline

What happened to this CVE, newest first.

2026
Affected products added · go toolchain/cmd/go
Oct 13, 2026 · CVE Program (cve.org) e CISA ADP
SSVC assessment updated
Oct 13, 2026 · CVE Program (cve.org) e CISA ADP
Record published
Oct 13, 2026
Fix documented
Oct 13, 2026 · NIST National Vulnerability Database
CVSS changed · 5.3
Oct 13, 2026 · NIST National Vulnerability Database
Source status changed · → Analyzed
Oct 13, 2026 · NIST National Vulnerability Database
Record created in this database
Oct 13, 2026 · NIST National Vulnerability Database
CVE published
May 7, 2026 · Go

Source activity

Repeated readings are counted rather than listed.

1× Official description updated · Oct 13, 2026 – Oct 13, 2026

References

4 on the record

pkg.go.dev/vuln/GO-2026-4978
Vendor Advisory, NIST National Vulnerability Database
go.dev/cl/763882
Patch, NIST National Vulnerability Database
go.dev/issue/78584
Issue Tracking, NIST National Vulnerability Database
groups.google.com/g/golang-announce/c/qcCIEXso47M
Issue Tracking, Mailing List, NIST National Vulnerability Database

Elsewhere on this site

Go toolchain
every CVE for this vendor

File handling
same class

CWE-59
other pages naming this weakness

Related CVEs (same products)

High CVE-2026-94447 Checksum database bypass for golang.org/toolchain in cmd/go 6d
High CVE-2026-94444 Checksum bypass for golang.org/fips140 in cmd/go 6d
Medium CVE-2026-42505 Invoking Encrypted Client Hello privacy leak in crypto/tls Jul 8, 2026
High CVE-2026-39822 Root escape via symlink plus trailing slash in os Jul 8, 2026
High CVE-2023-54365 Traefik - Denial of Service via HTTP/2 Request Handling Jun 23, 2026
High CVE-2026-42499 Quadratic string concatenation in consumePhrase in net/mail May 7, 2026

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.

Answered from this record

Text assembled only from the fields above — no additional claims.

What should defenders know first?

CVE-2026-39819 is "Invoking "go bug" follows symlinks in predictable temporary filenames in cmd/go", rated Medium. It affects Cmd/go (Go toolchain); versions are in the scope table. It is not in CISA KEV, which does not rule out exploitation. CVSS 5.3 describes technical severity. EPSS 0.15% estimates the probability of exploitation in 30 days; neither replaces your asset context. First verify whether exposed or business-critical assets run the affected versions, apply vendor fixes or mitigations, and preserve logs for review.

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