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FirefoxWeb browser · Mozilla

CVE-2023-4577

MEDIUM · 6.5 CVSS v3.1 Published 2023-09-11
Fix available
A fix is available. Upgrade to 115.2 / 117.0 or later.
See remediation →
72/100
Remediation priority · Elevated
Remotely reachable No privileges

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
When `UpdateRegExpStatics` attempted to access `initialStringHeap` it could already have been garbage collected prior to entering the function, which could potentially have led to an exploitable crash. This vulnerability affects Firefox < 117, Firefox ESR < 115.2, and Thunderbird < 115.2.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

Use-after-free vulnerability in Mozilla products where the UpdateRegExpStatics function accesses initialStringHeap after it has been garbage collected, potentially causing an exploitable crash.

MitigationUpgrade to Firefox 117+, Firefox ESR 115.2+, or Thunderbird 115.2+ to patch the vulnerability.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
FirefoxWeb browser
Affected:< 117.0
Firefox EsrWeb browser
Affected:< 115.2
ThunderbirdApplication
Affected:< 115.2

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
Required
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Identify installed Mozilla product
    Check if Firefox, Firefox ESR, or Thunderbird is installed by looking in the application's installation directory or program files. On Windows, check Add/Remove Programs or the application executable properties.
    Affected if Any of Firefox, Firefox ESR, or Thunderbird is present on the system
  2. Determine Firefox version
    For Firefox, type 'about:support' in the address bar or right-click the Firefox executable, select Properties, and view the Version field. On Linux, run 'firefox --version' in terminal.
    Affected if Firefox version is lower than 117.0
  3. Determine Firefox ESR version
    For Firefox ESR, type 'about:support' in the address bar or check the application version through system utilities. On Linux, run 'firefox-esr --version'. ESR versions typically include 'ESR' in the application name.
    Affected if Firefox ESR version is lower than 115.2
  4. Determine Thunderbird version
    For Thunderbird, type 'about:support' in the address bar or right-click the Thunderbird executable and view Properties. On Linux, run 'thunderbird --version'.
    Affected if Thunderbird version is lower than 115.2

You are affected if any installed Mozilla product matches these conditions: Firefox below 117.0, Firefox ESR below 115.2, or Thunderbird below 115.2.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 115.2 / 117.0 or later
Fixed in 115.2117.0
Interim mitigation

Upgrade to Firefox 117+, Firefox ESR 115.2+, or Thunderbird 115.2+ to patch the vulnerability.

Recommended fix High confidence

Firefox 117.0 or later; Firefox ESR 115.2 or later; Thunderbird 115.2 or later

  1. 1. Close all instances of Firefox, Firefox ESR, or Thunderbird
  2. 2. Open the application and navigate to the Help menu
  3. 3. Select 'About Firefox'/'About Thunderbird' to check current version
  4. 4. Click 'Check for Updates' to download and install the latest version
  5. 5. Restart the application after the update completes
  6. 6. Alternatively, download the latest version from https://www.mozilla.org/ for your specific product (Firefox, Firefox ESR, or Thunderbird)
  7. 7. Run the installer and follow the prompts to complete the upgrade
  8. 8. After installation, verify the version by checking About to confirm you are on 117.0+ (Firefox) or 115.2+ (Firefox ESR/Thunderbird)
Caveat Minor version upgrades typically do not introduce breaking changes for end users; review release notes for any behavior changes

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Firefox Scoped from the published advisory
  • Consultation1.0 h
  • Implementation2.0 h
  • Testing2.0 h
  • Review / QA1.0 h
6.0 hours of engineering $1,040
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $1,664.

Scan for this in your stack

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2023-4577 in production — separate from our analysis above.

No notes yet

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data