CVE-2026-5958

Arbitrary file overwrite via symlink TOCTOU race

Published Apr 20, 2026 · Updated Apr 20, 2026

TOCTOU race in GNU sed 4.1e through 4.9 allows local users to overwrite files through an attacker-controlled symlink swap. The open_next_file() function records the resolved output path through follow_symlink(), while ck_fopen() opens the original symlink path for input. Exploitation requires in-place editing with --follow-symlinks on an attacker-influenced path during the race window; resulting writes carry sed process permissions.

CVSS severity2.1
Low
EPSS probability0.14%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

TOCTOU race in GNU sed 4.1e through 4.9 allows local users to overwrite files through an attacker-controlled symlink swap. The open_next_file() function records the resolved output path through follow_symlink(), while ck_fopen() opens the original symlink path for input. Exploitation requires in-place editing with --follow-symlinks on an attacker-influenced path during the race window; resulting writes carry sed process permissions.

The record

CVE
CVE-2026-5958
Published
Apr 20, 2026
Updated
Apr 20, 2026
Vendor
The GnuPG Project
Product
GNU sed
Classifications
CWE-367, CAPEC-27, CAPEC-29, T1068
Attack vector
local
Privileges
unauthenticated

Timeline

How it unfolded

  1. Apr 20, 2026CVE publishedPublication date reported by the CVE source.
  2. Apr 20, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=4.1e <4.10

What conditions does exploitation require?

Attack vectorlocal
Required privilegesunauthenticated

What is affected?

The GnuPG Project · GNU sedversion=4.1e <4.10

Published CVSS scores

2.1CERT.PLCVSS:4.0/AV:L/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-367Time-of-check Time-of-use (TOCTOU) Race Condition
CAPEC-27Leveraging Race Conditions via Symbolic Links
CAPEC-29Leveraging Time-of-Check and Time-of-Use (TOCTOU) Race Conditions
T1068Exploitation for Privilege Escalation

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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