Regular Expression Denial of Service in httplib2
Priority LOW 39CWE-400Published · Updated
Key facts
- Attack vector
- Network
- Privileges required
- None
- User interaction
- None
- Attack complexity
- Low
- Impact type
- Denial of service
- Confidentiality · integrity · availability
- None · None · High
- Fix status
- Partial Red Hat: 1 fixed, 7 without a fix
Attack profile from CVSS 3.1 · CNA. Fix status from CNA, GitHub and Red Hat. Impact type from CWE-400.
Summary
httplib2 is a comprehensive HTTP client library for Python. In httplib2 before version 0.19.0, a malicious server which responds with long series of "\xa0" characters in the "www-authenticate" header may cause Denial of Service (CPU burn while parsing header) of the httplib2 client accessing said server. This is fixed in version 0.19.0 which contains a new implementation of auth headers parsing using the pyparsing library.
Why it matters now
EPSS 0.0367 89th percentileScored 2026-11-07
Public exploit Yes 1 exploit referenceTagged by NVD
Fix Partial httplib2 (httplib2): 0.19.0httplib2 (PyPI): 0.19.0Red Hat: 1 advisoryRed Hat: 1 fixed, 7 without a fix
SSVC decision points
Not available: CISA has not published SSVC decision points for this record.
Affected products
| Vendor | Product | Affected versions | Fixed in | Status | Source |
|---|---|---|---|---|---|
| httplib2 | httplib2 | before 0.19.0 | 0.19.0 | Patch available | CNA |
| — | httplib2 (PyPI) | before 0.19.0 | 0.19.0 | Patch available | GHSA-93xj-8mrv-444m |
- httplib2 Vendorhttplib2 Affected before 0.19.0 Fixed in 0.19.0 Patch available CNA
- httplib2 (PyPI) Vendor— Affected before 0.19.0 Fixed in 0.19.0 Patch available GHSA-93xj-8mrv-444m
Remediation
- Fix · CNA httplib2 (httplib2) Fixed in 0.19.0
- Fix · GHSA-93xj-8mrv-444m httplib2 (PyPI) Fixed in 0.19.0 Advisory →
Red Hat 1 advisory
- RHSA-2021:2116 Released 2021-05-26 · Red Hat rating ModerateRed Hat OpenStack Platform 16.1.6 (python-httplib2) security update
- Red Hat OpenStack Platform 16.1 python-httplib2-0.13.1-2.el8ost, python3-httplib2-0.13.1-2.el8ost
Vendor assessments
Red Hat
Red Hat rating: Low. Red Hat's page for this CVE →
| Product | Status | Plan or fix |
|---|---|---|
| Red Hat Ceph Storage 2 | Affected | No fix planned: Out of support scope |
| Red Hat Enterprise Linux 7 | Affected | No fix planned: Out of support scope |
| Red Hat Enterprise Linux 8 | Affected | No fix yet: Fix deferred |
| Red Hat OpenStack Platform 10 (Newton) | Affected | No fix planned: Out of support scope |
| Red Hat OpenStack Platform 13 (Queens) | Affected | No fix planned: Will not fix |
| Red Hat Storage 3 | Affected | No fix yet: Fix deferred |
| Red Hat Update Infrastructure 3 for Cloud Providers | Affected | No fix yet: Fix deferred |
| Red Hat OpenStack Platform 16.1 | Fixed | RHSA-2021:2116 |
Not affected: 1 product
- Red Hat Enterprise Linux 9
Timeline
- 2026-10-02 Threatist record created from CVE-2021-21240
- 2026-10-03 Alias added: GHSA-93xj-8mrv-444m
References
Patch 2
More Httplib2 vulnerabilities
- TI-2026-42746 httplib2: Decompression Bomb Denial of Service via Unbounded gzip/deflate Response Handling CVSS 3.1HIGH 7.5
- TI-2020-08952 CRLF injection in httplib2 CVSS 3.1MEDIUM 6.8
- TI-2013-01808 httplib2 0.7.2, 0.8, and earlier, after an initial connection is made, does not verify… CVSS 2.0LOW 2.6
Sources
- CVE-2021-21240 · CVE Program
- CVE-2021-21240 · NVD
- FIRST EPSS
- GHSA-93xj-8mrv-444m · GitHub Advisory Database · CC BY 4.0
- CVE-2021-21240 · Red Hat security data · CC BY 4.0
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