CVE-2026-35355: install TOCTOU Symlink Race (unlink-then-create Without Vulnerability

MODERATE
Advisory Identifier: GHSA-239g-2685-54x3
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CVSS 6.3
CWE-367 CWE-59
Published
Advisory Summary

CVE-2026-35355 is a MODERATE (CVSS 6.3) toctou symlink race (unlink-then-create without vulnerability (CWE-367: Time-of-check Time-of-use (TOCTOU) Race Condition) affecting install libraries in the crates.io ecosystem. The issue involves toctou symlink race (unlink-then-create without o_excl) allows arbitrary file overwrite. Remediation is available by upgrading affected packages to version 0.6.0.

CVE-2026-35355 at a Glance

CVE Identifier CVE-2026-35355
GHSA Identifier GHSA-239g-2685-54x3
Severity MODERATE
CVSS v3.1 Base Score 6.3
CWE Classification CWE-367: Time-of-check Time-of-use (TOCTOU) Race Condition
Affected Product install
Package Ecosystem crates.io
Published Date
Last Updated

Security Impact

CVSS: 6.3

The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:H).

Attack Vector Local (AV:L)
Attack Complexity High (AC:H)
Privileges Required Low (PR:L)
User Interaction None (UI:N)
Scope Unchanged (S:U)
Confidentiality None (C:N)
Integrity High (I:H)
Availability High (A:H)

How to Fix CVE-2026-35355

To remediate this vulnerability, upgrade all affected install dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

uu_install fixed: 0.6.0 
Upgrade uu_install to 0.6.0
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

inspect dependencies for uu_install

How to Check if You Are Affected

To determine whether your application is affected by CVE-2026-35355, inspect your project dependencies for install:

inspect dependencies for uu_install

Analyze the terminal output to locate any version of install in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 0.6.0), your application is affected.

Note: Verify declared build manifests and deployed runtime container environments.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-367: Time-of-check Time-of-use (TOCTOU) Race Condition, where the product checks the state of a resource before using that resource, but the resource's state can change between the check and the use in a way that invalidates the results of the check. In install, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

`copy_file` in `install/src/install.rs` removes the destination then recreates it by pathname via `File::create` / `fs::copy` without `O_EXCL`/`create_new`. Between the unlink and the recreate, a local attacker with write access to the destination directory can drop in a symlink and redirect the write. **Impact:** when `install` runs privileged into an attacker-writable directory (staging/build paths), the race allows redirecting writes to arbitrary files and overwriting sensitive system files (`/etc/passwd`, `/etc/shadow`). Recommendation: create atomically with `create_new`/`O_EXCL` and copy via the opened fd rather than reopening by path. **Remediation:** Acknowledged by Canonical; fixed in commit b5bbabc1. --- _Reported by Zellic in the *uutils coreutils Program Security Assessment* (prepared for Canonical, Jan 20 2026), audited commit `3a07ffc5a9bd4c283e75afa548ba1f1957bad242`. Finding 3.50. Credit: Zellic._

CVE-2026-35355 Affected install Versions

1 component(s)
Fixed Versions:
0.6.0
Product / Package Ecosystem Affected Versions Fixed Version
uu_install
 crates.io
< 0.6.0
0.6.0

References

GitHub Advisory / Wiki ADVISORY
https://github.com/uutils/coreutils/security/advisories/GHSA-239g-2685-54x3
NVD — CVE-2026-35355 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-35355
install Source Repository REPOSITORY
https://github.com/uutils/coreutils/pull/10067
Security Fix Commit FIX COMMIT
https://github.com/uutils/coreutils/commit/b5bbabc18a1121908848d836f869a4e98eb63886
install Source Repository REPOSITORY
https://github.com/uutils/coreutils
install Release RELEASE
https://github.com/uutils/coreutils/releases/tag/0.6.0

Frequently Asked Questions

What is CVE-2026-35355?
CVE-2026-35355 is a security vulnerability in install involving TOCTOU symlink race (unlink-then-create without O_EXCL) allows arbitrary file overwrite under CWE-367: Time-of-check Time-of-use (TOCTOU) Race Condition.
Which install versions are affected?
Affected versions include releases prior to 0.6.0 across affected packages: uu_install.
What version fixes CVE-2026-35355?
Upgrading to 0.6.0 (or the latest patched release for your respective branch) resolves the vulnerability.
Is uu_install affected?
Yes, uu_install is affected in releases prior to 0.6.0. Upgrade your dependency to 0.6.0 or later.
What is the CVSS score of CVE-2026-35355?
CVE-2026-35355 has a CVSS v3.1 base score of 6.3 (MODERATE) with vector string CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:H.
What CWE is associated with CVE-2026-35355?
CVE-2026-35355 is classified under CWE-367: Time-of-check Time-of-use (TOCTOU) Race Condition (The product checks the state of a resource before using that resource, but the resource's state can change between the check and the use in a way that invalidates the results of the check.).
How can I check crates.io dependencies for CVE-2026-35355?
Run the dependency tree command: 'inspect dependencies for uu_install'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-239g-2685-54x3",
  "modified" : "2026-07-06T19:54:08Z",
  "published" : "2026-07-06T19:54:08Z",
  "aliases" : [ "CVE-2026-35355" ],
  "summary" : "install: TOCTOU symlink race (unlink-then-create without O_EXCL) allows arbitrary file overwrite",
  "details" : "`copy_file` in `install/src/install.rs` removes the destination then recreates it by pathname via `File::create` / `fs::copy` without `O_EXCL`/`create_new`. Between the unlink and the recreate, a local attacker with write access to the destination directory can drop in a symlink and redirect the write.\n\n**Impact:** when `install` runs privileged into an attacker-writable directory (staging/build paths), the race allows redirecting writes to arbitrary files and overwriting sensitive system files (`/etc/passwd`, `/etc/shadow`). Recommendation: create atomically with `create_new`/`O_EXCL` and copy via the opened fd rather than reopening by path.\n\n**Remediation:** Acknowledged by Canonical; fixed in commit b5bbabc1.\n\n---\n_Reported by Zellic in the *uutils coreutils Program Security Assessment* (prepared for Canonical, Jan 20 2026), audited commit `3a07ffc5a9bd4c283e75afa548ba1f1957bad242`. Finding 3.50. Credit: Zellic._",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:H"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "crates.io",
      "name" : "uu_install"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "0.6.0"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/uutils/coreutils/security/advisories/GHSA-239g-2685-54x3"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-35355"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/uutils/coreutils/pull/10067"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/uutils/coreutils/commit/b5bbabc18a1121908848d836f869a4e98eb63886"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/uutils/coreutils"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/uutils/coreutils/releases/tag/0.6.0"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-367", "CWE-59" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-07-06T19:54:08Z",
    "nvd_published_at" : null
  }
}