vulnerability / NVI-00002669 / Revision 6
guzzlehttp/psr7: CRLF Injection in HTTP Start-Line Serialization
GitHub lists this reviewed advisory for guzzlehttp/psr7. Published version ranges and source prerequisites are shown below; this is not an inspection of a visitor’s application.
This report has not inspected your inventory, configuration, deployed build, reachability or evidence. A catalog listing and a severity score do not establish exposure or compromise.
01 / Meaning
Why it matters
Published affected context helps an owner decide what evidence to gather. This report has not examined your application.
4.8 medium
GitHub source severity; exploitability and local consequence require separate evidence.
As of · GitHub Advisory Database
4.8 MEDIUM (3.1)
security-advisories@github.com severity; no combined Null risk score.
0.229%
FIRST EPSS model v2026.06.15; exploitation probability over 30 days, percentile 0.13805. Missing scores are unknown.
As of · FIRST EPSS
02 / Applicability
The affected context
Affected versions, configuration prerequisites and known exclusions are public. Confirm each one against the deployed service.
guzzlehttp/psr7
source listed< 2.12.1
### Impact `guzzlehttp/psr7` did not reject CR/LF characters in certain first-party HTTP start-line fields: the request method, protocol version, and response reason phrase. If an application placed attacker-controlled data into one of those fields and later serialized the PSR-7 message as raw HTTP/1.x, for example with `Message::toString()` or an equivalent serializer, the serialized message could contain attacker-controlled header lines. The issue can also be reached through `Message::parseRequest()` or `Message::parseResponse()` when malformed raw messages are parsed into first-party PSR-7 objects and then serialized again. Creating or modifying a `Request`, `Response`, or other PSR-7 object alone is not sufficient. The issue requires the malformed message to be serialized and written to the network, forwarded, replayed, or otherwise processed by software that does not independently reject the malformed start line. This is not the normal request-sending path used by `guzzlehttp/guzzle`; applications using `guzzlehttp/psr7` only through Guzzle's standard HTTP client APIs are not expected to be affected. Applications are most likely to be affected when they manually serialize P
guzzlehttp/psr7
source listedECOSYSTEM: introduced 0; fixed 2.12.1
### Impact `guzzlehttp/psr7` did not reject CR/LF characters in certain first-party HTTP start-line fields: the request method, protocol version, and response reason phrase. If an application placed attacker-controlled data into one of those fields and later serialized the PSR-7 message as raw HTTP/1.x, for example with `Message::toString()` or an equivalent serializer, the serialized message could contain attacker-controlled header lines. The issue can also be reached through `Message::parseRequest()` or `Message::parseResponse()` when malformed raw messages are parsed into first-party PSR-7 objects and then serialized again. Creating or modifying a `Request`, `Response`, or other PSR-7 object alone is not sufficient. The issue requires the malformed message to be serialized and written to the network, forwarded, replayed, or otherwise processed by software that does not independently reject the malformed start line. This is not the normal request-sending path used by `guzzlehttp/guzzle`; applications using `guzzlehttp/psr7` only through Guzzle's standard HTTP client APIs are not expected to be affected. Applications are most likely to be affected when they manually serialize P
03 / Response
What to do next
- investigate
Identify the exact component and deployed version, examine the linked publisher’s conditions, and retain evidence of any mitigation.
Confirm current vendor support, compatibility and deployment evidence. This report has not tested a fix in your system. FIRST EPSS
- vendor patch
The original advisory lists fixed boundaries 2.12.1 for guzzlehttp/psr7. Confirm the publisher’s latest guidance.
Confirm current vendor support, compatibility and deployment evidence. This report has not tested a fix in your system. GitHub Advisory Database via OSV
A fixed release is not deployment evidence.
Check current vendor support and compatibility. After making a change, verify the deployed build and relevant runtime conditions. Keep the evidence, owner and time. An updated lockfile alone does not prove what is running.
04 / Limits
What this report cannot establish
- Customer inventory, deployment, reachability and exploitation have not been inspected.
- NVD lastModified does not establish freshness of every associated CPE record.
05 / Provenance
Sources you can inspect
Each assertion retains its source. Mirrored records may repeat one underlying publisher; additional links are not independent corroboration.
- GHSA-vm85-hxw5-5432 ↗
GitHub Advisory Database · vendor advisory
Observed . GitHub Advisory Database; CC-BY-4.0. Each advisory links its original attribution. Null normalizes fields.
- GHSA-vm85-hxw5-5432 ↗
GitHub Advisory Database via OSV · vendor advisory
Observed . GitHub-origin advisory, CC-BY-4.0; OSV is an aggregate copy, not independent corroboration.
- CVE-2026-55766 ↗
NIST National Vulnerability Database · official catalog
Observed . This product uses data from the NVD API but is not endorsed or certified by the NVD.
- CVE-2026-55766 ↗
FIRST EPSS · official catalog
Observed . FIRST EPSS; probability of exploitation in the next 30 days, not local compromise. Dataset date/model retained; FIRST services terms apply.
Public revision history
Only published revisions appear here. Routine fetches do not create a material-change event.
- Revision 6 ·
Dated EPSS estimate updated; this is not a new disclosure or proof of exploitation.
- Revision 5 ·
Source facts changed; compare the preserved prior revision.
- Revision 4 ·
Source facts changed; compare the preserved prior revision.
- Revision 3 ·
Dated EPSS estimate updated; this is not a new disclosure or proof of exploitation.
- Revision 2 ·
Dated EPSS estimate updated; this is not a new disclosure or proof of exploitation.
- Revision 1 ·
First indexed by Null; source disclosure date is shown separately.