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Mallory
Medium

RC4 Biases in TLS/SSL Plaintext Recovery

IdentifiersCVE-2013-2566CWE-327· Use of a Broken or Risky…

CVE-2013-2566 describes weaknesses in the RC4 stream cipher when used in TLS and SSL. RC4 exhibits multiple statistically significant single-byte biases in its keystream. When the same or partially predictable plaintext is transmitted across a large number of encrypted sessions, a remote attacker observing the ciphertext can apply statistical analysis to recover portions of the plaintext. The issue is not a memory corruption flaw in a specific implementation; it is a cryptographic weakness in the RC4 algorithm as deployed in TLS/SSL cipher suites.

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ANALYST BRIEF

Impact, mitigation & remediation

What it means. What to do now. Patch path, mitigations, and the assume-compromise checklist.

Impact

What an attacker gets, and what they’ve been doing with it.

Successful exploitation can allow partial plaintext recovery from encrypted TLS/SSL traffic protected with RC4-based cipher suites. This undermines confidentiality of sensitive data repeatedly transmitted in similar positions across many sessions, such as cookies, authentication tokens, or other predictable application-layer secrets. The attack is passive from the network perspective but requires substantial ciphertext collection and statistical processing.

Mitigation

If you can’t patch tonight, do this now.

If immediate remediation is not possible, reduce exposure by preventing negotiation of RC4 wherever configurable, prioritizing stronger cipher suites, and minimizing repeated transmission of identical secrets over many sessions. Prefer current TLS versions and hardened cipher configurations. However, the effective long-term mitigation is complete removal of RC4 support.

Remediation

Patch, then assume compromise.

Disable RC4 cipher suites in TLS/SSL configurations and migrate affected services and clients to modern cipher suites under TLS 1.2 or TLS 1.3. Update server, client, and intermediary TLS configurations so RC4 is no longer negotiated. Validate the effective configuration with TLS scanning or handshake testing tools to ensure no RC4 suites remain enabled.
PUBLIC EXPLOITS

Exploits

No public exploits tracked yet. Mallory keeps watching.

VALID 0 / 0 TOTALView more in app

No public exploit code observed for this vulnerability.

EXPOSURE SURFACE

Affected products & vendors

Products and vendors Mallory has correlated with this vulnerability. Open in Mallory to drill down to specific CPE configurations and version ranges.

VendorProductType
CanonicalUbuntu Linuxapplication
FujitsuM10-1 Firmwareoperating_system
FujitsuM10-4 Firmwareoperating_system
FujitsuM10-4s Firmwareoperating_system
FujitsuSparc Enterprise M3000 Firmwareoperating_system
FujitsuSparc Enterprise M4000 Firmwareoperating_system
FujitsuSparc Enterprise M5000 Firmwareoperating_system
FujitsuSparc Enterprise M8000 Firmwareoperating_system
FujitsuSparc Enterprise M9000 Firmwareoperating_system
MozillaFirefoxapplication
MozillaSeamonkeyapplication
MozillaThunderbirdapplication
MozillaThunderbird Esrapplication
OracleCommunications Application Session Controllerapplication
OracleHttp Serverapplication
OracleIntegrated Lights Out Manager Firmwareoperating_system

Vendor-confirmed product mapping. Mallory continuously reconciles this list against your asset inventory.

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Threat actor evidence

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Associated malware

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Detection signatures

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Vendor-by-vendor mapping

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Social activity

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