`http.cookiejar` applies expired `Set-Cookie` to cookie store before policy validation
- Exploited
- No known exploitation
- Fix
- Fixed in 3.16.0
- Who is exposed
- Not reported
Do first: Upgrade to a fixed version: 3.16.0.
- Last modified
- A 0-100 score for how much a CVE matters across the industry: exploitation, exposure, how widely the software is used, severity and whether a fix exists.What do these mean? →
- 23/100 · provisional
- Whether working attack code is public (Exploit-DB, Metasploit, Nuclei or GitHub). Public code makes attacks easier.What do these mean? →
- None on Exploit-DB, Metasploit or GitHub
Summary
A remote attacker can, without logging in and without any user action, make a malicious server's response delete cookies that belong to other domains from a shared cookie jar, such as the one used by urllib's HTTPCookieProcessor. The flaw is in Python's http.cookiejar module, which removed stored cookies when a response carried an already expired Set-Cookie header without first checking the cookie policy.
Written by anthropic/claude-haiku-5.5 from the sources below. Verify against them.
Read the original description
http.cookiejar.CookieJar deleted a stored cookie when a response carried an already expired Set-Cookie header for it, using the Domain and Path attributes from the header without consulting the cookie policy. A server could therefore delete cookies belonging to other domains from a shared cookie jar, such as the one used by urllib's HTTPCookieProcessor. The fix consults the cookie policy before an expired cookie may delete an existing one, as required by RFC 6265 section 5.3.
cve.now Index
- Exploitation?/40Unknown. No CISA SSVC exploitation rating yet
- Exposure17/25No login or user action needed per the CVSS vector, reachable over the network without a login · Unknown: No advisory context yet
- Reach?/20Unknown. No tracked technology or package matched
- Severity6.3/10CVSS 6.3
- No patch0/5No signal
What would change the score
- Would score about 68 if added to CISA KEV
- Would score about 63 if CISA's SSVC rates exploitation active
- Would score about 28 if advisories confirm default setups are exposed
What to do
Upgrade to a fixed version: 3.16.0.
Timeline
- CVE published
- First seen by cve.now
- Record last updated
Affected versions
- Python Software Foundation CPython
fixed in 3.16.0
Evidence 4
- Advisory
- Patch
- Report
- Link
Corrections
None so far.
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Questions about CVE-2026-124249
Is CVE-2026-124249 being exploited?
It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.Source: cve.now feed data
Which versions are affected by CVE-2026-124249?
CPython: before 3.16.0.Source: cve.now feed data
How do I fix CVE-2026-124249?
Upgrade to a fixed version: 3.16.0.Source: cve.now feed data