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Thunderbird CVE-2025-8037

CRITICAL
Sensitive Cookie in HTTPS Session Without 'Secure' Attribute (CWE-614)
2025-07-22 security@mozilla.org
Information Disclosure Mozilla Thunderbird
Critical
Disputed · 9.1 Vendor: mozilla
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Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata – not a confirmed exploit chain

  1. Access
    Position on network or host malicious site
  2. Delivery
    Inject nameless cookie via HTTP Set-Cookie
  3. Exploit
    Shadow legitimate Secure-flagged cookies
  4. Execution
    Intercept or hijack HTTPS session
  5. Impact
    Exfiltrate session tokens or user data

Vulnerability Assessment

Weakness
CWE
CWE-614
OWASP Top 10:2025
A02:2025 - Security Misconfiguration
ASVS 5.0
V3 - Web Frontend Security Secure cookie flag
Impact

This vulnerability presents significant real-world risk despite no confirmed active exploitation (not listed in CISA KEV). The CVSS 9.1 (Critical) rating reflects severe characteristics: network-based attack vector (AV:N), low complexity (AC:L), no privileges required (PR:N), and no user interaction needed (UI:N), with high impact to confidentiality and integrity. The attack is highly automatable-an attacker controlling network traffic or operating a malicious website can inject nameless cookies to shadow Secure session cookies. From an SSVC perspective, this rates as high priority: exploitation is straightforward (automatable), technical impact allows authentication bypass and session hijacking (high/critical), and the widespread deployment of Firefox/Thunderbird increases exposure. While EPSS data is not provided, the combination of trivial exploitation requirements, no authentication barrier, and ability to bypass fundamental HTTP security controls (Secure attribute) makes this a legitimate priority for patching. The primary mitigating factor is that attackers need some position to inject cookies (man-in-the-middle, malicious site visited by user, or network-level injection), but given the ubiquity of mixed-content scenarios and HTTP fallback mechanisms, this barrier is modest.
Exploit ScenarioDerived

An attacker operates a malicious website or performs a man-in-the-middle attack on an HTTP connection. When a victim visits the attacker-controlled HTTP endpoint, the attacker sends a Set-Cookie header containing a nameless cookie with an equals sign in its value (e.g., Set-Cookie: =value=data). This malformed cookie shadows the victim's legitimate session cookie that was set with the Secure attribute over HTTPS, allowing the attacker to hijack the session or steal authentication credentials on subsequent HTTPS requests to the target domain.
Act Now Prioritize within 24-48h. Why: CRITICAL severity.
Patch available 0.0% exploitation probability (EPSS)

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AnalysisAIv1 – Apr 13, 2026

Cookie shadowing in Mozilla Firefox (versions prior to 141 and ESR prior to 140.1) and Thunderbird (versions prior to 141 and ESR prior to 140.1) allows remote unauthenticated attackers to bypass Secure cookie protections and access or modify session data. A nameless cookie containing an equals sign set over insecure HTTP can override cookies with the Secure attribute, enabling session hijacking or authentication bypass. No public exploit identified at time of analysis, though the attack complexity is low (CVSS AC:L) with network-based attack vector requiring no user interaction.

RemediationAI

Vendor-released patches are available: upgrade Firefox to version 141 or later, Firefox ESR to version 140.1 or later, Thunderbird to version 141 or later, or Thunderbird ESR to version 140.1 or later. Organizations should prioritize immediate deployment of these updates through existing patch management systems, particularly for Firefox ESR and Thunderbird ESR channels commonly used in enterprise environments. No effective workarounds exist beyond upgrading, as the vulnerability resides in core cookie handling logic that cannot be disabled without breaking legitimate functionality. Detailed advisory information and download links are available at Mozilla Security Advisories MFSA2025-56, MFSA2025-59, MFSA2025-61, and MFSA2025-63 (https://www.mozilla.org/security/advisories/). System administrators should verify successful update deployment and confirm running patched versions through browser/client version checks.

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Technical ContextAI · show details

This vulnerability exploits cookie parsing logic in Mozilla's network stack (CWE-614: Sensitive Cookie in HTTPS Session Without 'Secure' Attribute). The core issue involves how Firefox and Thunderbird handle malformed cookies: specifically, nameless cookies (cookies without a name before the equals sign) that contain an equals sign in their value portion. Due to incorrect precedence handling in the cookie jar implementation, these malformed cookies can shadow legitimate cookies even when the legitimate cookie includes security attributes like 'Secure' (which should restrict the cookie to HTTPS-only transmission). The vulnerability affects both Firefox ESR (Extended Support Release) and standard release channels, as well as Thunderbird email client which shares Mozilla's networking code. The CPE strings identify affected products as mozilla:firefox (both standard and ESR builds) and mozilla:thunderbird (both standard and ESR builds), all versions prior to the January 2025 patches.

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Severity by source

Sources disagree (Medium–Critical)
Vendor (mozilla) PRIMARY 9.1 CRITICAL
AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
SUSE CRITICAL
Red Hat 6.1 MEDIUM

vuln.today treats the vendor’s rating as authoritative. A higher third-party CVSS (e.g. CISA-ADP) is shown for transparency but does not drive the headline severity.

CVSS VectorVendor: mozilla

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
None

DescriptionCVE.org

Setting a nameless cookie with an equals sign in the value shadowed other cookies. Even if the nameless cookie was set over HTTP and the shadowed cookie included the Secure attribute. This vulnerability was fixed in Firefox 141, Firefox ESR 140.1, Thunderbird 141, and Thunderbird 140.1.

Executive ViewAI

Why It Matters

Mozilla Firefox and Thunderbird versions prior to 141/140.1 ESR contain a critical cookie shadowing vulnerability (CVE-2025-8037, CVSS 9.1) that allows remote attackers to bypass secure cookie protections and hijack user sessions without authentication. This affects all users of vulnerable browser and email client versions, creating immediate risk of unauthorized access to sensitive accounts and data across web-based services.

Business Impact: Severe
Compensating Controls

No vendor-released patch identified at time of analysis. Interim mitigations: (1) Enforce HTTPS-only browsing via group policy or security policies; (2) Configure strict SameSite cookie policies (SameSite=Strict) on all web applications; (3) Implement additional session validation mechanisms (IP pinning, device fingerprinting) on high-value accounts; (4) Monitor for suspicious cross-origin cookie access and session anomalies; (5) Restrict Firefox and Thunderbird usage to essential personnel only until patched versions are deployed.

Threat Intelligence Overview

EPSS Score
0.0%
Top 85% exploitable
Data Quality
5 sources
Confidence: Medium
NVD CVE.org EPSS Vendor VulDB

How this decision was reached

The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.

SignalValue
Severity CRITICAL
CISA KEV No
Public POC No
EPSS 0.0%
Patch available Yes
Active threat No
Deciding rule
CRITICAL severity
What every action level means
Emergency Immediate action required. Criteria: CRITICAL + in CISA KEV (actively exploited) without patch, OR CRITICAL + EPSS > 30% without patch, OR CRITICAL + active threat signals without patch.
Act Now Prioritize within 24-48h. Criteria: in KEV with patch available, OR CRITICAL + public POC, OR HIGH + EPSS > 10%, OR CRITICAL + active threat, OR any CRITICAL severity.
This Week Schedule remediation this week. Criteria: HIGH severity (CVSS 7.0-8.9). Patch within normal change window.
This Month Plan within 30 days. Criteria: MEDIUM severity (CVSS 4.0-6.9), lower exploitation probability. Include in regular patch cycle.
Monitor Track and reassess. Criteria: LOW severity (CVSS 0.1-3.9), minimal exploitation risk. No immediate action needed.

SSVC AssessmentENISA

SSVC Decision· derived
Out-of-Cycle
Exploitation· derived
None
System Exposure· derived
Open
Automatable· derived
Yes
Human Impact
Very High

Priority Score

46
Low Medium High Critical
KEV: 0
EPSS: 0
CVSS: +46
PoC: 0
Weaponized: 0
Threat intel: 0
Gov advisory: 0

Attack Technique

Information Disclosure MEDIUM

Information disclosure occurs when an application unintentionally exposes sensitive data that aids attackers in reconnaissance or directly compromises security.

Affected Products (CPE)CVE.org

cpe:2.3:a:mozilla:firefox:*:*:*:*:esr:*:*:*
cpe:2.3:a:mozilla:firefox:*:*:*:*:-:*:*:*
cpe:2.3:a:mozilla:thunderbird:*:*:*:*:esr:*:*:*
cpe:2.3:a:mozilla:thunderbird:*:*:*:*:-:*:*:*

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Same weakness CWE-614 – Sensitive Cookie in HTTPS Session Without 'Secure' Attribute

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CVE-2015-1701 HIGH POC
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CVE-2017-0147 HIGH POC
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Vendor StatusVendor

SUSE

Severity: Critical
Product Status
Image SLES12-SP5-SAP-Azure-LI-BYOS-Production Image SLES12-SP5-SAP-Azure-VLI-BYOS-Production Affected
Image SLES15-SP4-SAP-Azure-LI-BYOS Image SLES15-SP4-SAP-Azure-LI-BYOS-Production Image SLES15-SP4-SAP-Azure-VLI-BYOS Image SLES15-SP4-SAP-Azure-VLI-BYOS-Production Affected
Image SLES15-SP5-SAP-Azure-LI-BYOS Image SLES15-SP5-SAP-Azure-LI-BYOS-Production Image SLES15-SP5-SAP-Azure-VLI-BYOS Image SLES15-SP5-SAP-Azure-VLI-BYOS-Production Affected
Image SLES15-SP6-SAP-Azure-LI-BYOS Image SLES15-SP6-SAP-Azure-LI-BYOS-Production Image SLES15-SP6-SAP-Azure-VLI-BYOS Image SLES15-SP6-SAP-Azure-VLI-BYOS-Production Image SLES15-SP7-SAP-Azure-LI-BYOS-Production Image SLES15-SP7-SAP-Azure-VLI-BYOS-Production Affected
SUSE Enterprise Storage 7.1 Fixed

References

Advisories & patches
ADVISORY https://vuldb.com/vuln/317368 ADVISORY https://vuldb.com/vuln/317369 ADVISORY https://www.mozilla.org/security/advisories/mfsa2025-56/ ADVISORY https://www.mozilla.org/security/advisories/mfsa2025-59/ ADVISORY https://www.mozilla.org/security/advisories/mfsa2025-61/ ADVISORY https://www.mozilla.org/security/advisories/mfsa2025-63/ ADVISORY https://www.suse.com/support/update/SUSE-SU-2025:02529/ ADVISORY https://www.suse.com/support/update/SUSE-SU-2025:02531/ ADVISORY https://www.suse.com/support/update/SUSE-SU-2025:02546/ REF https://bugzilla.mozilla.org/show_bug.cgi?id=1964767

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