CVE-2025-66418
ADVISORY - githubSummary
Impact
urllib3 supports chained HTTP encoding algorithms for response content according to RFC 9110 (e.g., Content-Encoding: gzip, zstd).
However, the number of links in the decompression chain was unbounded allowing a malicious server to insert a virtually unlimited number of compression steps leading to high CPU usage and massive memory allocation for the decompressed data.
Affected usages
Applications and libraries using urllib3 version 2.5.0 and earlier for HTTP requests to untrusted sources unless they disable content decoding explicitly.
Remediation
Upgrade to at least urllib3 v2.6.0 in which the library limits the number of links to 5.
If upgrading is not immediately possible, use preload_content=False and ensure that resp.headers["content-encoding"] contains a safe number of encodings before reading the response content.
Common Weakness Enumeration (CWE)
Allocation of Resources Without Limits or Throttling
Allocation of Resources Without Limits or Throttling
Allocation of Resources Without Limits or Throttling
GitHub
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CVSS SCORE
8.9high| Package | Type | OS Name | OS Version | Affected Ranges | Fix Versions |
|---|---|---|---|---|---|
| urllib3 | pypi | - | - | >=1.24,<2.6.0 | 2.6.0 |
CVSS:4 Severity and metrics
The CVSS metrics represent different qualitative aspects of a vulnerability that impact the overall score, as defined by the CVSS Specification.
The vulnerable component is bound to the network stack, but the attack is limited at the protocol level to a logically adjacent topology. This can mean an attack must be launched from the same shared physical (e.g., Bluetooth or IEEE 802.11) or logical (e.g., local IP subnet) network, or from within a secure or otherwise limited administrative domain (e.g., MPLS, secure VPN to an administrative network zone). One example of an Adjacent attack would be an ARP (IPv4) or neighbor discovery (IPv6) flood leading to a denial of service on the local LAN segment (e.g., CVE-2013-6014).
Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success when attacking the vulnerable component.
The successful attack depends on the presence of specific deployment and execution conditions of the vulnerable system that enable the attack. These include: A race condition must be won to successfully exploit the vulnerability. The successfulness of the attack is conditioned on execution conditions that are not under full control of the attacker. The attack may need to be launched multiple times against a single target before being successful. Network injection. The attacker must inject themselves into the logical network path between the target and the resource requested by the victim (e.g. vulnerabilities requiring an on-path attacker).
The attacker is unauthenticated prior to attack, and therefore does not require any access to settings or files of the vulnerable system to carry out an attack.
The vulnerable system can be exploited without interaction from any human user, other than the attacker. Examples include: a remote attacker is able to send packets to a target system a locally authenticated attacker executes code to elevate privileges.
There is no loss of confidentiality within the Vulnerable System.
There is no loss of confidentiality within the Subsequent System or all confidentiality impact is constrained to the Vulnerable System.
There is no loss of integrity within the Vulnerable System.
There is no loss of integrity within the Subsequent System or all integrity impact is constrained to the Vulnerable System.
There is a total loss of availability, resulting in the attacker being able to fully deny access to resources in the Vulnerable System; this loss is either sustained (while the attacker continues to deliver the attack) or persistent (the condition persists even after the attack has completed). Alternatively, the attacker has the ability to deny some availability, but the loss of availability presents a direct, serious consequence to the Vulnerable System (e.g., the attacker cannot disrupt existing connections, but can prevent new connections; the attacker can repeatedly exploit a vulnerability that, in each instance of a successful attack, leaks a only small amount of memory, but after repeated exploitation causes a service to become completely unavailable).
There is a total loss of availability, resulting in the attacker being able to fully deny access to resources in the Subsequent System; this loss is either sustained (while the attacker continues to deliver the attack) or persistent (the condition persists even after the attack has completed). Alternatively, the attacker has the ability to deny some availability, but the loss of availability presents a direct, serious consequence to the Subsequent System (e.g., the attacker cannot disrupt existing connections, but can prevent new connections; the attacker can repeatedly exploit a vulnerability that, in each instance of a successful attack, leaks a only small amount of memory, but after repeated exploitation causes a service to become completely unavailable).
NIST
3.9
CVSS SCORE
8.9highDebian
-
Ubuntu
3.9
CVSS SCORE
7.5mediumAmazon
-
CVSS SCORE
N/AmediumRed Hat
3.9
CVSS SCORE
7.5highChainguard
CGA-23fx-4vmh-cm8j
-
Chainguard
CGA-28h2-v62f-9558
-
Chainguard
CGA-2vfc-7392-8597
-
Chainguard
CGA-32cc-7wh3-48m8
-
Chainguard
CGA-44gw-7hgm-9hmj
-
Chainguard
CGA-4p44-29mm-47g9
-
Chainguard
CGA-5rv5-grgj-pwwc
-
Chainguard
CGA-6jg9-cgr2-8j65
-
Chainguard
CGA-6q42-3hjm-j46r
-
Chainguard
CGA-6r42-x94q-68w3
-
Chainguard
CGA-73v2-frpr-6cm7
-
Chainguard
CGA-8g68-52q3-g3j2
-
Chainguard
CGA-g3x3-hj9r-gmqr
-
Chainguard
CGA-h5hw-wfww-6f8h
-
Chainguard
CGA-jpwv-87r9-hgm6
-
Chainguard
CGA-p58r-fqwm-vfq4
-
Chainguard
CGA-phv4-9467-h3g4
-
Chainguard
CGA-qcpr-8xm5-jrgw
-
Chainguard
CGA-r5ph-cr34-78mp
-
Chainguard
CGA-rcmx-fv9w-4c28
-
Chainguard
CGA-vqfh-frf6-9crh
-
Chainguard
CGA-vx33-8fv6-fpfg
-
Chainguard
CGA-w59h-375r-3v44
-
Chainguard
CGA-xx74-9j94-h268
-
minimos
MINI-2j5j-mx6v-5v36
-
minimos
MINI-7fh3-8hwm-xq38
-
minimos
MINI-86rf-527g-vj73
-
minimos
MINI-cw83-g2m8-hqfv
-
minimos
MINI-fcqc-vwm2-6257
-
minimos
MINI-m2f3-vrqw-wh79
-
minimos
MINI-qqqr-7wqv-2qf5
-
minimos
MINI-vq9w-8629-wf7g
-