Hash DoS

Hash collision denial of service.

Python 2.7 and older and Python 3.2 and older require the -R command line option to enable the enable hash function randomization. Randomization is enabled by default since Python 3.3 (the -R option is ignored).

“Effective Denial of Service attacks against web application platforms” talk at the CCC: 2011-12-28

See also the PEP 456: Secure and interchangeable hash algorithm: Python 3.4 switched to SipHash.

  • Ruby: CRuby 1.9 fixed the vulnerability in 2008 with randomized hash function; JRuby has also been fixed.
  • Perl: Perl 5.8.1 fixed the vulnerability in 2003 using a random “PERL_HASH_SEED”.

Dates:

  • Disclosure date: 2011-12-28 (CCC talk)
  • Reported by: Alexander “alech” Klink and Julian “zeri” Wälde

Fixed In

Python issue

Hash collision security issue.

  • Python issue: bpo-13703
  • Creation date: 2012-01-03
  • Reporter: Barry A. Warsaw

CVE-2012-1150

Python before 2.6.8, 2.7.x before 2.7.3, 3.x before 3.1.5, and 3.2.x before 3.2.3 computes hash values without restricting the ability to trigger hash collisions predictably, which allows context-dependent attackers to cause a denial of service (CPU consumption) via crafted input to an application that maintains a hash table.

Timeline

Timeline using the disclosure date 2011-12-28 as reference:

  • 2011-12-28: Disclosure date (CCC talk)
  • 2012-01-03 (+6 days): Python issue bpo-13703 reported by Barry A. Warsaw
  • 2012-02-20 (+54 days): commit 2daf6ae (branch 2.7)
  • 2012-02-21 (+55 days): commit 1e13eb0 (branch 2.6)
  • 2012-04-06 (+100 days): Python 3.1.5 released
  • 2012-04-09 (+103 days): Python 2.7.3 released
  • 2012-04-10 (+104 days): Python 2.6.8 released
  • 2012-04-10 (+104 days): Python 3.2.3 released
  • 2012-09-29: Python 3.3.0 released
  • 2012-10-05 (+282 days): CVE-2012-1150 published