CVE-2013-3587: 
Apache HTTP Server vulnerability analysis and mitigation

The BREACH (Browser Reconnaissance & Exfiltration via Adaptive Compression of Hypertext) vulnerability (CVE-2013-3587) affects the HTTPS protocol when used with HTTP compression. The vulnerability allows man-in-the-middle attackers to obtain plaintext secret values by observing length differences during a series of guesses where a string in an HTTP request URL potentially matches an unknown string in an HTTP response body (CERT VU, BREACH Attack).

The attack requires several conditions to be met: 1) HTTPS-enabled endpoint with stream ciphers like RC4 or block ciphers with adaptive padding, 2) The attacker must be able to measure the size of HTTPS responses, 3) Use of HTTP-level compression (e.g. gzip), 4) A request parameter that is reflected in the response body, 5) A static secret in the body (e.g. CSRF token), and 6) A relatively static response. The attack works by making a series of requests with different guesses and observing compression ratios to deduce secret values. A successful attack can be executed with approximately 1,000-4,000 requests within 30 seconds (CERT VU).

When successfully exploited, this vulnerability allows attackers to recover sensitive information like CSRF tokens, session IDs, and other secret values from encrypted HTTPS traffic. This can lead to session hijacking, account compromise, and other security breaches. The vulnerability affects a wide range of web applications that use both HTTPS and HTTP compression (BREACH Attack).

Several mitigation strategies are recommended: 1) Disable HTTP compression, 2) Separate secrets from user input, 3) Randomize secrets in each client request, 4) Mask secrets by XORing with a random secret per request, 5) Protect pages with CSRF protections, 6) Add random padding to responses to obscure length differences. For example, Django recommends disabling GZip middleware and web server compression modules (Django Blog, CERT VU).

The vulnerability received significant attention after its presentation at Black Hat USA 2013. Major web frameworks like Django issued security advisories and recommended mitigations. Red Hat noted that their Enterprise Linux 5 and 6 httpd packages were not vulnerable by default as DEFLATE compression was not enabled in the default configuration (Red Hat Bugzilla).