CVE-2015-8805 – This vulnerability is an implementation flaw in... (How to Fix)

Q: What is the severity of CVE-2015-8805?

CVE-2015-8805 has a CVSS score of 9.8 (CRITICAL). This vulnerability is an implementation flaw in Nettle's P-256 elliptic curve cryptography that produces incorrect cryptographic output due to improper carry propagation. Attackers could potentially compromise cryptographic operations like TLS/SSL connections, digital signatures, or key exchanges that rely on this flawed implementation. Systems using Nettle library versions before 3.2 for P-256 operations are affected.

📋 TL;DR

This vulnerability is an implementation flaw in Nettle's P-256 elliptic curve cryptography that produces incorrect cryptographic output due to improper carry propagation. Attackers could potentially compromise cryptographic operations like TLS/SSL connections, digital signatures, or key exchanges that rely on this flawed implementation. Systems using Nettle library versions before 3.2 for P-256 operations are affected.

💻 Affected Systems

Products:

Nettle cryptographic library
Applications linking against Nettle
Systems using GnuTLS (which uses Nettle)

Versions: All versions before 3.2

Operating Systems: Linux distributions including Red Hat, SUSE, Debian, Ubuntu, Any OS using vulnerable Nettle versions

Default Config Vulnerable: ⚠️ Yes

Notes: Only affects systems using P-256 elliptic curve operations. Applications must be using the vulnerable ecc_256_modq function.

📦 What is this software?

⚠️ Risk & Real-World Impact

🔴

Worst Case

Complete compromise of cryptographic security leading to man-in-the-middle attacks, decryption of sensitive communications, forged digital signatures, or unauthorized access to protected systems.

🟠

Likely Case

Cryptographic failures in TLS/SSL connections, invalid digital signatures, or compromised key exchanges that could lead to data interception or authentication bypass.

🟢

If Mitigated

Limited impact if proper network segmentation, monitoring, and alternative cryptographic controls are in place, though cryptographic integrity remains compromised.

🌐 Internet-Facing: HIGH

🏢 Internal Only: MEDIUM

🎯 Exploit Status

Public PoC: ✅ No

Weaponized: UNKNOWN

Unauthenticated Exploit: ⚠️ Yes

Complexity: MEDIUM

Exploitation requires understanding of elliptic curve cryptography and ability to trigger the vulnerable function. No public exploit code is documented.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: Nettle 3.2 and later

Vendor Advisory: http://rhn.redhat.com/errata/RHSA-2016-2582.html

Restart Required: Yes

Instructions:

1. Update Nettle library to version 3.2 or later using your distribution's package manager. 2. For Red Hat/CentOS: 'yum update nettle'. 3. For Debian/Ubuntu: 'apt-get update && apt-get install nettle'. 4. Rebuild or restart applications using Nettle. 5. Verify the update with 'nettle-hash --version' or check package version.

🔧 Temporary Workarounds

Disable P-256 elliptic curve usage

all

Configure applications to use alternative elliptic curves (like P-384 or P-521) instead of P-256

Depends on specific application configuration

🧯 If You Can't Patch

Implement network segmentation to isolate vulnerable systems
Enable enhanced monitoring for cryptographic failures and unusual authentication patterns

🔍 How to Verify

Check if Vulnerable:

Check Nettle version: 'nettle-hash --version' or 'rpm -q nettle' or 'dpkg -l | grep nettle'. If version is below 3.2, system is vulnerable.

Check Version:

nettle-hash --version

Verify Fix Applied:

Confirm Nettle version is 3.2 or higher: 'nettle-hash --version' should show 3.2+. Test cryptographic operations using P-256.

📡 Detection & Monitoring

Log Indicators:

Cryptographic operation failures
TLS/SSL handshake failures
Digital signature verification errors

Network Indicators:

Unusual patterns in encrypted traffic
Failed cryptographic negotiations

SIEM Query:

Search for cryptographic error messages or failed authentication events involving P-256 operations

📊 Metadata

CVE ID: CVE-2015-8805

CVSS v3 Score: 9.8 (CRITICAL)

CVSS Vector: CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

CWE: CWE-310

Published: February 23, 2016

Last Updated: April 12, 2025

🔗 References

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