CVE-2011-1521

CVE-2011-1521 is a medium-severity vulnerability in Python with a CVSS 2.0 base score of 6.4. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-399.

Key facts

• Severity: Medium (CVSS 2.0 base score 6.4)
• EPSS exploit prediction: 4% (90th percentile)
• Actively exploited: Not listed in CISA KEV
• Weakness: CWE-399
• Affected product: Python
• Published: 2011-05-24
• Last modified: 2026-06-16

Description

The urllib and urllib2 modules in Python 2.x before 2.7.2 and 3.x before 3.2.1 process Location headers that specify redirection to file: URLs, which makes it easier for remote attackers to obtain sensitive information or cause a denial of service (resource consumption) via a crafted URL, as demonstrated by the file:///etc/passwd and file:///dev/zero URLs.

Frequently asked questions

What is CVE-2011-1521?

The urllib and urllib2 modules in Python 2.x before 2.7.2 and 3.x before 3.2.1 process Location headers that specify redirection to file: URLs, which makes it easier for remote attackers to obtain sensitive information or cause a denial of service (resource consumption) via a crafted URL, as demonstrated by the file:///etc/passwd and file:///dev/zero URLs.

How severe is CVE-2011-1521?

CVE-2011-1521 has a CVSS 2.0 base score of 6.4, rated medium severity.

Is CVE-2011-1521 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 4% (90th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2011-1521?

CVE-2011-1521 primarily affects Python. In total, 39 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2011-1521?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

When was CVE-2011-1521 published?

CVE-2011-1521 was published on 2011-05-24 and last updated on 2026-06-16.

References

• http://bugs.python.org/issue11662
• http://hg.python.org/cpython/file/96a6c128822b/Misc/NEWS
• http://hg.python.org/cpython/file/b2934d98dac1/Misc/NEWS
• http://hg.python.org/cpython/rev/96a6c128822b/
• http://hg.python.org/cpython/rev/b2934d98dac1/
• http://lists.apple.com/archives/Security-announce/2011//Oct/msg00003.html
• http://lists.opensuse.org/opensuse-security-announce/2011-05/msg00005.html
• http://openwall.com/lists/oss-security/2011/03/24/5
• http://openwall.com/lists/oss-security/2011/03/28/2
• http://openwall.com/lists/oss-security/2011/09/11/1
• http://openwall.com/lists/oss-security/2011/09/13/2
• http://openwall.com/lists/oss-security/2011/09/15/5
• http://secunia.com/advisories/50858
• http://secunia.com/advisories/51024
• http://secunia.com/advisories/51040
• http://securitytracker.com/id?1025488
• http://support.apple.com/kb/HT5002
• http://www.mandriva.com/security/advisories?name=MDVSA-2011:096
• http://www.ubuntu.com/usn/USN-1592-1
• http://www.ubuntu.com/usn/USN-1596-1
• http://www.ubuntu.com/usn/USN-1613-1
• http://www.ubuntu.com/usn/USN-1613-2
• https://bugzilla.redhat.com/show_bug.cgi?id=690560
• https://bugzilla.redhat.com/show_bug.cgi?id=737366
• https://www.djangoproject.com/weblog/2011/sep/09/
• https://www.djangoproject.com/weblog/2011/sep/10/127/

Affected products (39)

• cpe:2.3:a:python:python:2.0:*:*:*:*:*:*:*
• cpe:2.3:a:python:python:2.0.1:*:*:*:*:*:*:*
• cpe:2.3:a:python:python:2.1:*:*:*:*:*:*:*
• cpe:2.3:a:python:python:2.1.1:*:*:*:*:*:*:*
• cpe:2.3:a:python:python:2.1.2:*:*:*:*:*:*:*
• cpe:2.3:a:python:python:2.1.3:*:*:*:*:*:*:*
• cpe:2.3:a:python:python:2.2:*:*:*:*:*:*:*
• cpe:2.3:a:python:python:2.2.1:*:*:*:*:*:*:*
• cpe:2.3:a:python:python:2.2.2:*:*:*:*:*:*:*
• cpe:2.3:a:python:python:2.2.3:*:*:*:*:*:*:*
• cpe:2.3:a:python:python:2.3.1:*:*:*:*:*:*:*
• cpe:2.3:a:python:python:2.3.2:*:*:*:*:*:*:*
• cpe:2.3:a:python:python:2.3.3:*:*:*:*:*:*:*
• cpe:2.3:a:python:python:2.3.4:*:*:*:*:*:*:*
• cpe:2.3:a:python:python:2.3.5:*:*:*:*:*:*:*
• cpe:2.3:a:python:python:2.3.7:*:*:*:*:*:*:*
• cpe:2.3:a:python:python:2.4.1:*:*:*:*:*:*:*
• cpe:2.3:a:python:python:2.4.2:*:*:*:*:*:*:*
• cpe:2.3:a:python:python:2.4.3:*:*:*:*:*:*:*
• cpe:2.3:a:python:python:2.4.4:*:*:*:*:*:*:*
• cpe:2.3:a:python:python:2.4.6:*:*:*:*:*:*:*
• cpe:2.3:a:python:python:2.5.1:*:*:*:*:*:*:*
• cpe:2.3:a:python:python:2.5.2:*:*:*:*:*:*:*
• cpe:2.3:a:python:python:2.5.3:*:*:*:*:*:*:*
• cpe:2.3:a:python:python:2.5.4:*:*:*:*:*:*:*
• cpe:2.3:a:python:python:2.6.1:*:*:*:*:*:*:*
• cpe:2.3:a:python:python:2.6.4:*:*:*:*:*:*:*
• cpe:2.3:a:python:python:2.6.5:*:*:*:*:*:*:*
• cpe:2.3:a:python:python:2.6.6:*:*:*:*:*:*:*
• cpe:2.3:a:python:python:2.6.7:*:*:*:*:*:*:*
• cpe:2.3:a:python:python:2.7.1:*:*:*:*:*:*:*
• cpe:2.3:a:python:python:3.0:*:*:*:*:*:*:*
• cpe:2.3:a:python:python:3.0.1:*:*:*:*:*:*:*
• cpe:2.3:a:python:python:3.1:*:*:*:*:*:*:*
• cpe:2.3:a:python:python:3.1.1:*:*:*:*:*:*:*
• cpe:2.3:a:python:python:3.1.2:*:*:*:*:*:*:*
• cpe:2.3:a:python:python:3.1.3:*:*:*:*:*:*:*
• cpe:2.3:a:python:python:3.2:*:*:*:*:*:*:*
• cpe:2.3:a:python:python:3.2:alpha:*:*:*:*:*:*

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Other CWE-399 (Resource Management Errors) vulnerabilities

• CVE-2015-8104 — Critical (CVSS 10.0): The KVM subsystem in the Linux kernel through 4.2.6, and Xen 4.3.x through 4.6.x, allows guest OS users to cause a…
• CVE-2015-0339 — Critical (CVSS 10.0): Adobe Flash Player before 13.0.0.277 and 14.x through 17.x before 17.0.0.134 on Windows and OS X and before…
• CVE-2015-0335 — Critical (CVSS 10.0): Adobe Flash Player before 13.0.0.277 and 14.x through 17.x before 17.0.0.134 on Windows and OS X and before…
• CVE-2015-0333 — Critical (CVSS 10.0): Adobe Flash Player before 13.0.0.277 and 14.x through 17.x before 17.0.0.134 on Windows and OS X and before…
• CVE-2014-4121 — Critical (CVSS 10.0): Microsoft .NET Framework 2.0 SP2, 3.5, 3.5.1, 4, 4.5, 4.5.1, and 4.5.2 does not properly parse internationalized…
• CVE-2014-0560 — Critical (CVSS 10.0): Use-after-free vulnerability in Adobe Reader and Acrobat 10.x before 10.1.12 and 11.x before 11.0.09 on Windows and OS…

Browse all CWE-399 (Resource Management Errors) vulnerabilities →

Threat intelligence

Threat-intel indicators referencing this CVE:

• 121.164.135.251 (ipv4-addr)